review article the study of neutrino oscillations with emulsion...

Hindawi Publishing CorporationAdvances in High Energy PhysicsVolume 2013 Article ID 382172 17 pageshttpdxdoiorg1011552013382172

Review ArticleThe Study of Neutrino Oscillations with Emulsion Detectors

A Ereditato

Albert Einstein Center for Fundamental Physics Laboratory for High Energy Physics University of Bern Sidlerstrasse 53012 Bern Switzerland

Correspondence should be addressed to A Ereditato antonioereditatocernch

Received 8 July 2013 Accepted 17 November 2013

Academic Editor Leslie Camilleri

Copyright copy 2013 A Ereditato This is an open access article distributed under the Creative Commons Attribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Particle detectors based on nuclear emulsions contributed to the history of physics with fundamental discoveries The experimentsbenefited from the unsurpassed spatial and angular resolution of the devices in the measurement of ionizing particle tracks andin their identification Despite the decline of the technique around the 1970rsquos caused by the development of the modern electronicparticle detectors emulsions are still alive today thanks to the vigorous rebirth of the technique that took place around the beginningof the 1990rsquos in particular due to the needs of neutrino experimentsThis progress involved both the emulsion detectors themselvesand the automatic microscopes needed for their optical scanning Nuclear emulsions have marked the study of neutrino physicsnotably in relation to neutrino oscillation experiments and to the related first detection of tau-neutrinos Relevant applications inthis field are reviewed here with a focus on the main projects An outlook is also given trying to address the main directions of theRampD effort currently in progress and the challenging applications to various fields

1 Introduction to Nuclear Emulsions

Particle detectors based on the nuclear emulsion techniquecontributed to the history of particle physics with fundamen-tal discoveries and measurements that profited from theirunsurpassed spatial and angular resolution in the measure-ment of charged elementary particle tracksMoreover thanksto specific detector arrangements accurate momentum andenergy measurements were also carried out Despite thedecline of the technique around 1960ndash1970 due to the devel-opment and use of the modern electronic particle detectorsemulsions are still used today thanks to the vigorous rebirthof the technique that took place around the beginning of the1990rsquos driven by the needs of neutrino experiments

Nuclear emulsions have been effectively used in manyparticle physics experiments and in particular contributedto neutrino oscillation physics and to the related issue ofthe detection of tau-neutrinos (]

120591) Here focus is on this

specific physics subject and will unfortunately exclude themany scientific results that were obtained in other differentfields For those we recommend the reader to consultexisting reviews [1ndash3] The reader is also invited to notethat the emulsion detection technique is based on twoindependent aspects that have been synergic throughout

their technological development the emulsion detector itselfand the devices (microscopes) necessary for extracting theinformation stored in the emulsions

An emulsion usually consists of a huge number of crystalsof silver bromide (AgBr) dispersed in gelatin Light orionizing particles passing through an emulsion can activatesome of the silver ldquograinsrdquo This process is rather complexand details can be found in the above-mentioned reviewpapers As a result the absorption of energy in the crystalof silver bromide leads to the concentration of a few silveratoms into an aggregate that can act as a development centerhence creating a latent image at this point still invisibleA physicochemical process then allows transforming thosegrains into metallic silver After a suitable developmentprocedure the silver halide emulsion is placed into a bath(fixer) that only leaves the small black granules of silver Thedetection of space-correlated sequences of these granules bysuitable optical microscopes allows measuring the trajectoryof ionizing particles The role of the gelatin is to providea three-dimensional matrix that allows to locate the smallcrystals of the halide and to prevent them from migratingduring the development and fixation procedures This looksvery similar to what happens for normal photographic filmsHowever nuclear emulsions are different from the latter

2 Advances in High Energy Physics

for several reasons for the higher content of silver halide(by about one order of magnitude) for the larger thickness(sim times100) and for the smaller size and more uniform silvergrains

Several quantities characterize nuclear emulsions as aparticle detector At first their sensitivity related to thenumber of grains that are produced for a given energy releaseby an incoming particle The second feature is the so-calledfadingThis is the oxidation process that causes the reductionof the number of ldquostoredrdquo grains along the track as a functionof time High relative humidity and temperature could accel-erate fading leading to the loss of detectable tracks As wewill see fading was exploited for recent applications in orderto ldquocleanrdquo emulsions prior to their use erasing unwantedaccumulated cosmic-ray and environmental radiation tracksThe third factor is the mechanical distortion of the emulsionlayersThis occurs either locally or globally and can obviouslyaffect the knowledge of the absolute position of particletracks and more seriously their direction and curvatureHowever several effective techniques exist and are routinelyemployed to reduce distortions and their effects Finallyrandom distributed grains (the so-called ldquofogrdquo) producedby thermal excitation constitute a background for trackrecognition in the emulsion This potential background fortrack identification and reconstruction is usually quantifiedby the number of (fog) grains present per 1000 120583m3 Figure 1shows an electron microscope image of the silver crystals inthe emulsion gel and the reconstructed image of a minimumionizing particle track (MIP) The sensitivity corresponds toabout 30 grains100120583m

2 A Brief History

Emulsions have a long history The first use of the detectordates to the pioneering work of Kinoshita [4] and later onby Powell et al [5] who got important results in the 1950rsquosby profiting from the continuous progress in the productionof gel with improved quality The discovery of the pion in1947 constituted an outstanding success of the technique[6] An important breakthrough was represented by theinvention of the so-called Emulsion Cloud Chamber (ECC)(Figure 2) In the ECC emulsion films or thicker plates areinterspaced by passive material layers made of plastic ormetal constituting what we would call today a sampling-calorimeter In this way one can potentially fully reconstructall tracks of an electromagnetic or hadronic shower With theECC arrangement emulsions became high space-resolutiontracking devices with full 3D reconstruction capabilities inaddition to the ldquostandardrdquo use as a pure volumeimagingdetector Similar sandwich arrangements were proposed evenbefore the advent of the ECC technique as reported in [2]

The study of events taken with ECC detectors profitsfrom the potential reconstruction of all tracks producedin a primary interaction occurring in the passive materialSpace angles are measured for track segments and showerenergy and axis reconstruction is performed as well Particledecays can be identified by detecting kinks in the tracksMoreover by exploiting Multiple Coulomb Scattering andemulsion ionization measurements one can obtain accurate

measurements of the particle momenta In the early timesthe mechanical stability of the ECC sandwich was generallyensured by a vacuum packing paper known as ldquoorigamirdquoalso needed to protect the films from the external lighthumidity and polluting gases Film-to-film alignment can beperformed by suitable X-ray exposure As we will see lateron with the OPERA experiment the ECC technique reachedits highest development with several insights and innovativetechnological solutions

The ECC was first developed and used by Kaplon tostudy heavy primaries in cosmic-ray interactions [7] ECCdetectors were then applied to the study of the cosmic-rayspectrum and to very high energy interaction processesNishimura who contributed significantly to the developmentof the technique proposed the ECC for the measurementof the energy of 120574-rays through the study of the inducedelectromagnetic shower and proposed the method of tuningthe development of electron showers by a suitable use ofpassive material plates [8] Still in Japan and in collaborationwith the FUJI companyNiu proposed double-sided emulsionplates where the sensitive emulsion is deposited on either sideof a plastic base [3] The optical properties of the base werechosen to be close to those of the emulsion gel (meta-acryliclucite) The use of a plastic base between the two emulsionlayers allows the precise measurement of the incident particletrack angle by connecting grains near the base which are notaffected by distortions (Figure 3)

With ECC detectors the emulsion technique got animpressive boost due to the possibility of realizing largesize (surface and volume) detectors specially for cosmic-raydetection thanks to the use of dense metal plates comple-menting the outstanding tracking properties of the emulsionlayers One canmention in particular the Chacaltaya [9] andtheMt Fuji [10 11] experiments and inmore recent times theRUNJOB [12] and JACEE [12] detectors

Thanks to an experiment conducted with an ECC detec-tor placed on a cargo flight in 1971 Niu et al discoveredthe so-called X-particles [13] by observing a cosmic-rayinduced event where two charged particles produced in aprimary interaction exhibit a clearly identified kink decay-topology (Figure 4) Today we know that that event had tobe attributed to charmed meson production and decay Thishappened three years before the discovery of the 119869Ψ particleby the groups of Richter and Ting with electronic detectors ataccelerators More information on Niursquos results can be foundin [3] and references therein

With the advent of the electronic particle detectors onestarted using ECCs in conjunction with electronic deviceswith the main purpose of giving to some extent time-resolution to the emulsions through proper association oftracks reconstructed ldquoat the same timerdquo in both detectorsalthough with a different spatial resolution We talk in thiscase of a hybrid experimental setup Thanks to the electronicdetectors tracks originated by particles interacting in theECC are preselected to approximately identify the positionwhere to start the emulsion scanning or look for interactionvertices as shown in Figure 2 The consequent emulsionscanning allows accurately measuring and studying theevents with much higher space accuracy (see eg [14])

Advances in High Energy Physics 3

(a)

100120583

m

(b)

Figure 1 (a) Silver grains (02120583m) in the emulsion gel (b) Track produced by a minimum ionizing particle About 30 grains100 120583m aredetected by the optical microscope performing the measurement

Cosmic raysfor internalalignmentcalibration

Emulsion Lead ECCCS

Scintillationdetector

film plate

Figure 2 Schematic drawing of an ECC detector One can see the track segments produced by a neutrino interacting in one of the passivemetal plates Also shown are tracks induced by cosmic-rays that can be used for the film-to-film precision alignment The downstreamscintillator detector and interface emulsion layers (CS) can be used in specific applications to drive the reconstruction of the event tracksstarting from the most downstream emulsion layer

For this ldquostep-by-steprdquo event reconstruction procedure onecould introduce a further intermediate phase by employingadditional thin emulsion films originally called changeablesheets (CS) to act as an intermediate interface between theelectronic tracker and the actual emulsions of the ECCThe CS concept was first applied in the E531 experiment atFermilab [14]

The CS detector arrangement is shown in Figure 5 as itis being used for the OPERA experiment Scintillator-stripplanes identify some of the particle tracks produced in theinteraction of a primary particle in the ECC sandwich Thesetracks are then extrapolated to the CS interface films that arescanned to search for track segmentsmatching the scintillatorpredictions Only if this correspondence is validated theECC detector is unpacked its emulsion films developed andscanned to search for the primary interaction For severalapplications the CS detectors were periodically replaced

during the physics runs in order to limit the integration ofbackground tracks and to facilitate the identification of tracksfound in the electronic detectors

In the 1970rsquos emulsion detectors of increasing massand complexity were developed for applications to particlephysics experiments conducted at particle accelerators withhybrid setups Emulsions were used as active targets withhigh space-resolution combined with electronic trackerscalorimeters and spectrometers used to pre-select or triggerspecific events in the emulsions and to complement theemulsion-based kinematical information Important for ourdiscussion emulsion experiments were successfully designedand operated to study neutrino interactions As one of thefirst examples one can mention the observation in 1976 ofthe decay of a charmed particle produced in a high-energyneutrino interactions in a Fermilab experiment [15] Anotherexperiment performed at CERN in 1977 used emulsions


Emulsion layersMicrotrack

Base-track

Plastic base Microtrack

Figure 3 Schematics of the reconstruction of double emulsionlayer tracks The points close to the plastic base allow a precisemeasurement of the track angles since they are not affected bydistortions

coupled to the large bubble chamber BEBC exposed to aneutrino beam [16] More than 500 charged current neutrinointeractions in the emulsions were identified 8 of themattributed to neutrino-produced charmed particles

The already mentioned E531 experiment was originallyproposed to study charmed particles produced in neutrinointeractions The result on the cross-section measurementsare given in [17] and the measurement of the lifetime ofcharmed particles is reported in [18ndash21] The active neu-trino target consisted of nuclear emulsions where short-livedparticles could be detected with micrometric accuracy Thedecay products were measured by means of an electronicspectrometer thus making E531 the first hybrid particlephysics experiment 122 events were tagged by the presence ofa secondary vertex in the target 119 induced by neutrinos and3 by antineutrinos Events with a charmed hadron in the finalstate were studied in detail in order to detect the presence ofheavily ionizing particles (baryons) and fully reconstruct thekinematics at the decay vertex Among those events 57 wereclassified as D0 candidates [22] One important side result ofE531 was a sensitive search for neutrino oscillations [23 24]

The excellent capability of hybrid emulsion experimentsin the detection of short-lived particles was exploited inmanyprojects that yielded outstanding science contributions Onecan mention in particular the CERNWA75 experiment withthe first direct observation of the production and decay of Bmesons [25] and the Fermilab E653 experiment aimed at themeasurement of B meson lifetime [26] in addition to otherseveral studies conducted with proton and nucleus-nucleusinteractions (see [3] for a review)

This ability of the emulsion technique in the measure-ment of short-lived particles was an asset for the studiesstarted around the 1990rsquos which involved neutrino beams inparticular for the detection of tau-neutrinos either promptlyproduced or coming from the oscillation process Howeverbefore attacking this subject it is worth describing the parallelprogress of the emulsion scanning methods and technologythat made feasible such studies

3 Modern Emulsion Detectors

The progress of the emulsion plate and film technologyhas been very much driven by the applications notably for

the detection of short-lived particles and in the contextof this review for the need of identifying tau-leptons Thelatter in turn can be indication of the charged currentinteraction of tau-neutrinos either prompt (eg from abeam dump experiment) or coming from the oscillation ofmuon neutrinos as in the case of the dominant channelfor the so-called atmospheric neutrino-mixing signal [27]We will review these experiments later on Here one cansummarize the main technological advances that made theseexperiments feasible

An important milestone was met by fulfilling the require-ments of the CHORUS neutrino oscillation experimentat CERN [28 29] The hybrid detector was based on anunprecedented amount of nuclear emulsions to be used asan active target for the interaction of tau-neutrinos possiblygenerated from muon-neutrino oscillations The emulsiontarget had a mass of 770 kg segmented into four stackseach consisting of eightmodules individually composed of 36plates with a surface of 36 times 72 cm2 The plates had a plasticsupport of 90 120583m coated on either side with emulsion layersof 350 120583m thickness [29] CHORUS represented a milestonein the history of nuclear emulsions for the size of the targetand of the related CS interfaces also massively used in theexperiment The realization of the target required labor-intensive procedures for emulsion gel production manualpouring of the plastic bases and development conductedin the CERN emulsion laboratory [30] originally proposedfor the CERN WA75 experiment This effort progressed inparallel to the development of the required analysis toolsin primis of the first automatic scanning microscopes asdescribed in the next section

With the conceptual proposal and initial design of theOPERA experiment [31 32] we assisted in thematerializationof original ideas meant for the realization of an unprece-dented use of the ECC technique for neutrino oscillationexperiments [33] The project determined a consequent rev-olution in the technique Emulsions transformed from activebulk target detectors realized and assembled by researchersat typical laboratory scales into industrially produced filmsthought as high-resolution microtracking devices assembledin a large number of ECCunitsThis effortwas very successfulthanks to the collaboration between the Nagoya group ledby Niwa and the FUJI company [34] together with otherrelevant industrial contributions One should mention inparticular the realization of the sim10 million lead plates withhigh mechanical uniformity the automatic assembly of thesim150000 ECC detectors constituting the OPERA target byrobotized assembly lines working underground at LNGSthe large film developing stations at the LNGS and thechangeable sheet production line operational in one of theunderground LNGShalls A description of these complex andlarge-scale infrastructure can be found in [35]

Very uniform automated machine coating of 44 120583memulsion layers on either side of a 250120583m plastic base wassuccessfully achieved on the huge scale of about 10 millionfilms each of about 10 times 125 cm2 for a total emulsion surfaceof nearly 110000m2 In order to allow for the automaticindustrial coating the gel needed to be diluted in order


40

35

30

25

20

15

10

9

0 0

138 cm

350 cm

B B

D (C)(C)

(B)(B) AA D1205870

1205870

Plat

e num

ber

10120583m

B998400 B998400C998400 C998400

X projection Y projection

(a)

A

B

D

1205870

C

B998400

C998400

10 120583m

Z projection

(b)

Figure 4 Original drawing of Niursquos event representing the first evidence for the production and decay of short-lived X (charmed) particlesin cosmic-ray interactions

102mm

128mm

79mm

ECCbrick

264mm

Target tracker(scintillator strip)

Changeable sheetthickness 3mm

Figure 5 Principle of a hybrid detector constituted by electronictrackers emulsion film interfaces (CS) and ECC modules

to reduce its viscosity This implied a reduction of thegrain density in turn recovered by improvements in the gelsensitivity obtained for example by a controlled double-jet method for the production of mono-dispersion of AgBrmicrocrystals The number of crystals along the particletrajectories was increased by keeping constant the volumeoccupancy ofAgBr and the average diameter of the crystals Amulti-coating of the films was adopted by FUJI after the first

Emulsion layer

Plastic base (205120583m)

Figure 6 Microphotography of the cross-section of an OPERAemulsion film Two 44120583m thick emulsion layers are coated on aplastic base of 205120583m One can also notice the 2 120583m thick coatingfilms in the middle of each layer

20120583m layer is coated on both sides of a rolled plastic base asecond layer is coated over the first one A thin 2 120583m gelatinspacer protects adjacent emulsion layers A FUJI OPERAfilmis shown in Figure 6

Another development that made the OPERA experi-ment feasible was the realization of the so-called emulsionrefreshment High temperature and high relative humidityincrease the rate of the progressive loss of the latent imageAs mentioned above this process is called fading Thispossibility however might even be useful when the exposureoccurs much later than the (large scale) film production anda low background is required as in the case of OPERAFading of the OPERA films after production and storage


(a) (b)

Figure 7 OPERA emulsion film not treated with ldquorefreshingrdquo (a) and after ldquorefreshingrdquo (b) The background goes down from sim30 to lt1tracksmm2

timewas achieved by introducing 5-methylbenzotriazole intothe emulsion gel [34] Absorption of this compound by thesilver specks induced by radiation decreases the oxidationreduction-potential while the sensitized centers of sulfurand gold remain stable against oxidation In this way mostof the tracks recorded after production (due to ambientradioactivity and cosmic-rays) are erased still maintaining ahigh enough sensitivity of the refreshed films A typical cycleconsists of three days at 98 relative humidity and 27∘C Sucha procedure allows erasing more than 95 of all accumulatedtracks This is illustrated in Figure 7 that shows a film treatedwith refreshing compared to another one not refreshed

Finally a few words on the continuing RampD on theemulsion gel technology We will see in the following thatspecific applications demand gel with improved sensitivityand efficiency features Somework is in progress in particularin Nagoya where gels of different characteristics can beproduced in the laboratory In Figure 8 one can see pho-tographs of emulsions films realized and tested in Bern byemploying custom-made emulsion gel fromNagoya and fromthe Russian company Slavic It is clear that one can achieveperformances appreciably better than those obtained forthe large-scale production of the OPERA experiment Theseresults will open the way to several other developments andto the precision tuning of the emulsion properties tailored tothe specific application

4 Modern Emulsion Scanning Systems

In 1974 a great progress in the emulsion scanning technologytook place with the introduction of tomographic readoutof the emulsion layers by the Nagoya group [36] todaystill leader in the exploitation and development of emulsiondetectors and scanning devices If the thickness of theactive layer is appreciably larger than the focal depth of themicroscope optics (10ndash20 times) one can acquire multiple(tomographic) pictures of the layer by moving step-by-stepthe objective along the direction orthogonal to the emulsionsurface Suitably combining the images one could be ableto identify and reconstruct tracks of particles traversing

the layer (Figure 3) A first microscope system based onthis approach was successfully employed for the readout ofthe CS of the E653 experiment at Fermilab In that case16 tomographic images of the emulsion layer were takenthanks to a TV tube used as image grabber The techniquewas further developed by replacing the video by a CCDcamera and introducing an FPGA-based processor This ledto the so-called Track Selector system continuously operatedand updated by the Nagoya group and used for a series ofexperiments [37]

With the advent of semiautomatic (operator-assisted) andfully-automatic scanning the emulsion detection technologygot a consequent boost given the largely increased numberof events (or equivalently of emulsion surface) that couldbe analyzed for a given time interval The scanning speedwas limited by the time needed for the computer-controlledmovement of the objective lenses to reach the different focalpositions due to the waiting time in turn required to dampmechanical vibrations that become relevant when dealingwith micrometric accuracies The following generations ofthe original Track Selector system improved substantiallywith time [38] The system was complemented by a fullyautomatic data offline analysis applied after the digitizationof the individual tracks around a given angleThis feature wasmade possible by the availability of fast electronics and CCDsand of more and more performing stage mechanics Theso-called net-scan method [39] also developed in Nagoyaeventually allowed for the reconstruction of tracks by associ-ating all detected track segments independently of their angleand allowed complete event reconstruction [40] momentumdetermination by Multiple Coulomb Scattering [41 42] andelectron identification by shower analysis [43 44]

The presently running version of the Track Selector the S-UTS [45] based on the use of highly customized componentsfeatures impressive performance and bears testimony to theoutstanding work conducted in Nagoya in the course ofabout twenty years (Figure 9) For the S-UTS one of themain design features is the removal of the stop-and-goprocess of the stage in the image data taking which as saidabove is the mechanical bottleneck of the first originallydeveloped systems The objective lens moves at the same


Reference (OPERA film)

GD 303FD 101

Nagoya gel

GD 477FD 19

Russian gel

GD 330FD 5410

0120583

m

Figure 8 Example of results obtained with different emulsion gels GD stands for grain density and FD for fog density The new ldquoNagoyardquogel is very promising as indicated by the measured features

Scan

ning

spee

d (c

m2h

)

100

10

11

01

001

0001

0003

0082

72

CHORUS DONUT OPERATS (TTL) NTS (CPLD) UTS (FPGA) SUTS (FPGA)

Figure 9 Time evolution of the scanning speed of the Track Selectorsystem in relation to themain experiments of applicationThe speedis measured in square centimeters of emulsion surface scanned perhour

(constant) speed as the stage while moving along the verticalaxis and grabbing images with a very fast CCD camera Apiezoelectric device drives the optical system A frontendimage processor makes zero-suppression and pixel packingA dedicated processing board performs track recognitionbuilds microtracks and stores them in a temporary deviceThe routine scanning speed of the S-UTS is of more than20 cm2hourlayer while one of the S-UTS systems hasreached the speed of 72 cm2houremulsion layer by usinga larger field of view without deteriorating the intrinsicmicrometric accuracy of the emulsion films

Another scanning system was originally developed bythe Salerno group [47] This seminal work eventually led tothe currently used European Scanning System (ESS) [48ndash50]intended for the OPERA experiment Also the ESS employscommercial subsystems in a software-based framework Themicroscope is a Cartesian robot holding the emulsion filmon a horizontal stage with a CMOS camera mounted on the

vertical optical axis along which it can be moved to vary thefocal plane with a step equal to the focal depth of about 3 120583mThe control workstation hosts a motion control unit thatdirects the stage to span the area to be scanned and drives thecamera along the vertical axis to produce optical tomographicimage sequences The stage is moved to the desired positionand the images are grabbed after it stops with a stop-and-go algorithmThe images are grabbed by a Megapixel cameraat the speed of 376 frames per second while the camera ismoving in the vertical direction The whole system can workat a speed analogous to the standard S-UTS Microscopesbased on the S-UTS and on the ESS are shown in Figure 10

Regarding the future developments one canmention twomain lines of research The first one is the further upgradeof Nagoyarsquos S-UTS system RampD studies are in progress withthe ambitious goal of reaching a scanning speed of more thana few hundred square centimeters per hour [3] The idea isbased on the use of commercial steppers used for lithographyand Megapixel cameras with high frame (gt60 fps) and highpixel readout rates (gt370Mpixelss)The steppers can providea space resolution better than 350 nm and an exposure fieldlarger than 20 times 20mm2

Another approach very recent is being considered bothin Japan and in Europe which features the use of GraphicProcessor Units (GPUs) This approach constitutes a sort ofrevolution in the reconstruction of emulsion data State-of-the-art GPUs are envisioned such as the NVIDIA GeForceTITAN with a power of about 46 Teraflops with 2688processing cores in one GPU while even a modern CPUwith 6 cores (of the type i7-3960X) corresponds to only 016Teraflops A further advantage of this approach is that theachievable performance is scalable with the number of GPUsThis idea was proposed by Ariga [51] in Bern where thisdevelopment is presently being actively followed By nowseveral other groups are investigating the possibilities offeredby the use of GPUs for a further step in the development ofautomatic emulsion scanning One canmention in particularthe work done by the Toho [52] and by the Nagoya groupswhich by using dedicated optics and 72 GPUs has shown


(a) (b)

Figure 10 (a) Photograph of one of the Nagoya S-UTS scanning systems (b) The Bern scanning laboratory equipped with five ESSmicroscopes with the associated automated film changers [46]

the possibility of reaching a scanning speed equivalent to10000 cm2 of emulsion surface per hour

5 CHORUS and DONUT

Neutrino mixing means that the neutrino flavor eigenstatesinvolved in weak interaction processes (]

119890 ]120583and ]

120591) can

be expressed as a superposition of mass eigenstates (withmass eigenvalues 119898

1 1198982and 119898

3) through a rotation and

unitary mixing matrix called Pontecorvo-Maki-Nakagawa-Sakata (PMNS) [53ndash55] The occurrence of mixing generatesoscillations of neutrinos propagating in space and timenamely the periodic variation of their flavor compositionprovided that neutrinos have nondegenerate mass eigen-values The parameters characterizing oscillations are threemixing angles similarly to what happens for quark mass andweak eigenstates through the CKM matrix and two masseigenvalue squared differences Δ1198982

13= 1198982

3minus 11989821and

Δ119898212= 11989822minus 11989821 in addition to a possible CP violating

phase term in the matrix [27] The oscillatory flavor conver-sion probability also depends on the ratio 119871119864 between thedistance traveled by the neutrinos before detection and theirenergyThe latter parameter can in principle be chosen whendesigning the experiment in order to place the detector(s)in the condition of actually measuring the appearance of adifferent flavor absent in the beam or the disappearance ofneutrinos of the initial flavor

Following theoretical arguments developed around thebeginning of the 1990rsquos favoring the ]

120591as a constituent of

the Dark Matter of the Universe (provided it could have amass of 1ndash10 eV2) the neutrino community started arguingthat searching for neutrino oscillations (from muon- to tau-neutrinos) could be a powerful method to identify such amassive neutrino It should be noted that at that timenodirectevidence existed yet for the ]

120591The alreadymentioned CHO-

RUS experiment [28] was designed with this twofold goalto search for neutrino oscillations in the parameter region

Interaction

Decay

120591

120591

120583

120583minus120591minus

Figure 11 Schematics of the production anddecay topology of a tau-lepton produced in CHORUS by a tau-neutrino possibly generatedin the oscillation of the muon neutrinos of the CERNWANF beam

corresponding to a 1ndash10 eV2 ]120591mass and to provide the first

evidence for the detection of this elusive leptonThis could beaccomplished by a so-called short baseline experiment withthe detector placed at about 1 km distance from the source ofhigh-energy neutrinos with the right distance and energy todevelop a signal of ]

120583rarr ]120591oscillations corresponding to

a ]120591in the 1ndash10 eV2 mass rangeNuclear emulsions played a key role in the design of

the experiment The goal was the detection of the veryshort track of the 120591 lepton coming from the charged currentinteraction of a ]

120591 in turn produced by the oscillation of

a ]120583constituting the neutrino beam For this one could profit

from the use of the dense high space-resolution emulsions torealize a hybrid detector well suited to a high sensitivity studyof the decay topologies of the 120591 (Figure 11) Emulsions couldalso allow the full reconstruction of the event kinematics inturn required for background suppressionThis approachwassupported and justified by the advances in the emulsion tech-nique mainly in relation to the handling of large quantities ofemulsions and also thanks to the above-mentioned progress


Beam

Anticounter

ShieldingFibre

trackers

Emulsion targetsand fibre trackers

Hexagonalmagnet

High resolutioncalorimeter

H ST

Spectrometer

120583

TV

sim15m

Figure 12 Schematic drawing of the CHORUS apparatus The large emulsion target was contained in a temperature-controlled cold roomincluding the emulsion stacks the changeable sheets the fiber tracker planes together with their optoelectronic readout chains and the aircore hexagonal magnet Downstream a fiber-lead calorimeter and iron muon spectrometers complement the experimental setup

in the emulsion scanning and offline analysis such to reducethe analysis time of the emulsions by orders of magnitude ascompared to the early times

The hybrid CHORUS apparatus combined a large nuclearemulsion target previously described with various electronicdetectors Since charmed particles and the 120591 lepton havesimilar lifetimes the detector was also well suited for theobservation of the production and decay of charm a source ofbackground for the oscillation search but also an interestingphysics subject per se The very large emulsion stacks werefollowed by a set of scintillating fiber planes Three CSdetectors with a 90120583m emulsion layer on both sides of a800120583m thick plastic base were used as interface between thefiber trackers and the ldquobulkrdquo emulsion The accuracy of thetracker prediction in the CSwas about 150 120583m in position and2mrad in track angle

The electronic detectors downstream of the emulsiontarget and its associated trackers included a hadron spec-trometer measuring the bending of charged particles withan air-core magnet a high-resolution calorimeter wherethe energy and direction of showers were measured and amuon spectrometerTheCHORUS apparatus is schematicallydepicted in Figure 12 and a photograph taken during itsinstallation is shown in Figure 13

The operation of the experiment consisted of severalsteps It is worth noting that the large-size emulsion targetwas replaced only once during the entire duration of theexperiment while the CS were periodically exchanged withnew detectors therefore integrating background tracks for arelatively short period A much better time resolution wasobviously provided by the electronic detectors With the CSscanning the association between electronic detectors andemulsions takes place and tracks with position and anglecompatible with that of the electronic trackersrsquo predictions

Figure 13 Photograph of the CERN hall during the installation ofthe CHORUS (bottom right) andNOMAD (top left) detectors alongthe WANF muon neutrino beam

are searched for in the interface emulsions If found thesetracks are further extrapolated into the bulk emulsion with amuch better spatial resolution up to the track stopping pointwith the above-mentioned scan-back procedure consistingin connecting emulsion layers progressively more upstreamAfter that a ldquovolume scanrdquo (net-scan) around the presumedvertex is accomplished and repeated for all stopping tracksuntil the neutrino interaction vertex is found In the searchfor charmed particle decays a dedicated topological selectionwas applied to the collected net-scan data The analysisprocedure was complemented by the visual inspection of theselected event candidates aimed at checking both primaryand secondary vertices making use of the ldquostackrdquo configura-tion Decay topologies could be well separated from ordinarynuclear interactions since the latter usually exhibit fragments


Figure 14 Exclusion plot showing the final result of the CHORUSexperiment in the search for ]

120583rarr ]120591oscillations The parameter

region corresponding to a ]120591as Dark Matter candidate is excluded

down to relatively small values of the corresponding mixing angleThe CHORUS result is compared to the one obtained by theNOMAD experiment running in parallel in the WANF beam line

from nuclear break-up or so-called ldquoblobsrdquo from nuclearrecoil

More than 100000 neutrino interactions were identified(located) andmeasured in the emulsions of CHORUSUnfor-tunately the search for oscillations was negative and just anupper limit to the oscillation probability was eventually set[56] The negative result is illustrated in Figure 14 whichshows the so-called exclusion plot indicating the region ofthe oscillation parameter excluded by the experiment atthe 90 confidence level The vertex of a muon neutrinointeraction in one CHORUS emulsion stack is shown inFigure 15 Figure 16 illustrates an eventwith a topology similarto that of a 120591 lepton due to the production and decay ofa charmed particle The study of neutrino induced charmevents has been one of themain side results of the experimentA large statistics of sim2000 fully neutrino-induced charmedhadron event vertices was gathered with the outstandingreconstruction features provided by the emulsion detectorsWith such events CHORUS has been able to measure the Λ

119888

and D0 exclusive production cross-section [57] the double-charm production cross-section in neutral and charged cur-rent interactions [58] and the associated charm production[59]

As said above CHORUS represented a milestone in thehistory of nuclear emulsions for the size of the target and ofthe CS detectors for the complexity of the related technicalfacilities as well as for the great challenge represented bythe unprecedented event statistics All major internationalemulsion groups from Japan Italy Korea and Turkey partic-ipated in the experiment The convergence of virtually all theavailable worldwide expertise (apart from several emulsiongroups from Russia) substantially contributed to the success

Figure 15 Photograph of neutrino vertex (interaction point) in theCHORUS emulsionsThe imagemicroscope image size correspondsto about 100 times 100 120583m2 The neutrino was travelling perpendicularto the emulsion plate Heavily ionizing large angle track point to theneutrino interaction point

of the project and to the already mentioned rebirth of thetechniqueThis is also confirmed by the fact that other groupsand individuals formerly not working on emulsion detectorssoon got acquainted with the technique providing valuabletechnical and scientific contributions

A high-sensitivity follow-up of the CHORUS experimentwas then proposed at CERN with the goal of increasing bymore than one order of magnitude its sensitivity in the mea-surement of the oscillationmixing-angle still as suggested bya scenario where the tau-neutrino could be a Dark Mattercandidate The conceptual idea was first discussed in [60] Inthat case emulsions were proposed as large-surface trackersfor the high-resolution measurement of hadron and muonmomentaThis idea was then incorporated in the proposal ofthe TOSCA experiment [61] The project at the end was notrealizedmainly because of the growing evidence for neutrinooscillations with atmospheric neutrinos first provided by theKamiokande [62] and then by the Super-Kamiokande exper-iments [63] in a complementary region of the oscillationparameters characterized by a large mixing angle and a verysmall value of the Δ1198982 oscillation parameter related to themass eigenvalues of the oscillating neutrinos

In parallel it was considered important to directlyobserve the ]

120591 whose existence although indirectly estab-

lished was still not firmly proven by an appearance exper-iment The first direct detection of the ]

120591was the scientific

goal of the Fermilab DONUT experiment [64 65] Oncemore nuclear emulsions were considered for the identifica-tion of tau-leptons in turn produced in the charged currentinteraction of tau-neutrinosThe latter were promptly createdin the decay of D

119904mesons produced in a 800GeV proton

beam dump Also in this case we have to notice the keycontribution of the Nagoya group joined by other Japaneseemulsion groups

An ironemulsion ECC target was adopted in DONUTto provide large mass for neutrino interactions and the

Advances in High Energy Physics 11Be

am ax

is (120583

m)

800

700

600

500

400

300

200

100

0

2001000minus200 minus100

Emulsionlayer

Emulsionlayer

Acetate base

h120583+ 120583minusRun 874 Event 978 Z-projection

Figure 16 Reconstructed charm event in CHORUS The view isabout 400 times 400 120583m2 The neutrino comes from the bottom ofthe picture The event is similar to one possibly induced by a tau-neutrinoThe short track of the charmedparticle (light blue) exhibitsthe distinctive kink topology due to the decay into an undetectedneutrinoThe presence of an identified prompt negative muon track(red dots) bymeans of the downstream spectrometer strongly favorsthe charm event hypothesis

identification of the interaction vertex through the detectionof the millimetric track of the tau prior to its decay TheECC target was complemented by fiber trackers (analogouslyto CHORUS) to help in the track extrapolation into theemulsions The DONUT experiment allowed identifying 578neutrino interactions with 9 signal candidate events for anestimated background of 15 events This constituted thediscovery of the tau-neutrino in the year 2000 One of thesignal candidate events is shown in Figure 17 The shorttrack of the tau (about 300 120583m long) is clearly exhibitingthe characteristic kink unambiguous signature of a decaytopology over the much less probable large-angle hadron ormuon scattering

6 OPERA The Largest Nuclear EmulsionDetector Ever

The solution of the long-standing solar and atmosphericneutrino anomalies came from a series of crucial experimentsconducted in the last two decades that led to the discoveryof neutrino oscillations (see eg [20]) The occurrence ofoscillations and the consequent existence of a finite (althoughvery small) mass for the neutrinos is in contrast to what isassumed in the Standard Model of particles and interactionsoscillations are so far the only evidence for new physicsbeyond the Standard Model

Around the end of the 1990rsquos the scientific debate aroundneutrino oscillations became very intense The indicationsfrom experiments involving atmospheric and solar neutrinoswere more and more convincing until the unambiguous

FL = 280120583m120579kink = 90mradp = 46+16minus04 GeVcpT = 041+014minus008 GeVc

Figure 17 Schematic display of a candidate ]120591event detected by the

ECC emulsion detector of the DONUT experiment The identifica-tion of 9 such events with a 15 event background constituted thediscovery of the tau-neutrino [66 67]

discovery by the already mentioned Super-Kamiokandeexperiment [63] pointing to the occurrence of ]

120583rarr

]120591oscillations At that time there was a general consensus on

the need for a confirmation of the oscillation signal obtainedwith atmospheric neutrinos by experiments exploiting man-made neutrino beams but sensitive to the same parameterregion As mentioned above this could be achieved througha suitable choice of theLE parameterThe results fromSuper-Kamiokande and the other experiments with atmosphericneutrinos indicated a value of Δm2 around 10minus3 eV2 muchsmaller than the sim10 eV2 region explored by CHORUS

The conceptual idea of the OPERA experiment [31 32]contrary to other approaches looking for the disappearanceof an initial neutrino flavor flux coming from an acceleratoror from a nuclear reactor was based on the possibility ofdetecting the direct appearance of oscillations in the ]

120583rarr

]120591channel as indicated by the Super-Kamiokande atmo-

spheric neutrino signal Similarly to CHORUS looking forappearance turned into the need of identifying the short-lived tau-lepton with a ldquovertex detectorrdquo of several thousandtons mass because of the large distance required fromsource to detector to develop an oscillation signal given thesmall value of Δm2 The only realistic possibility was theadoption of nuclear emulsions (high space resolution) usedin the ECC configuration (high target mass) since a fullysensitive emulsion target a la CHORUS would have beenunrealistically expensive and even impossible to produceThe detection principle of the experiment is described inFigure 18

The idea of OPERA was to exploit a long baselineaccelerator neutrino beam with L of the order of 1000 kmcombined with a relatively high neutrino energy (⟨119864⟩ sim17GeV) such to determine the ldquocorrectrdquo LE ratio and to beabove the kinematical threshold (sim35GeV) for producing therelatively heavy 120591 lepton This concept materialized into thedesign of an experiment to be hosted at LNGS the largestunderground physics laboratory in the world about 730 kmaway from the neutrino beam source at CERNThe dedicatedCNGS neutrino beam was produced by the interaction of


Pb Emulsion layers

Interface films (CS)

ECC brick

Electronicstrackers

120591

120591

1mm

Figure 18 Schematic view of the detection principle of OPERA (notto scale) Electronic trackers and changeable sheets are used in seriesto predict the neutrino interaction point in one of the nearly 150000ECC units (bricks) that compose the target of the experiment The120591 kink decay-topology is identified by high-accuracy emulsion filmssandwiched in the bricks

Figure 19 Photograph of the OPERA detector at the LNGS Onecan recognize the two SuperModules (target and spectrometers) andsome empty slots in the target after removal of ECC bricks

primary protons from the CERN SPS onto a carbon targethence (mostly) producing pions and kaons The decay ofthese mesons into neutrinos generates the long baselineneutrino beam directed to the detector at LNGS

As in CHORUS the 120591 has to be identified by the detectionof its characteristic decay topologies in one prong (electronmuon or hadron) or in three prongs This is done with alarge number of ECC units made of 1mm thick lead platesinterspacedwith thin emulsion films acting as high-accuracytracking devices contrary to the role of active target thatemulsions had inCHORUSThe fullOPERAdetector ismadeof two identical Super Modules each consisting of a targetsection of about 900 tons made of ECC modules (bricks) ofa scintillator tracker detector needed to prelocalize neutrinointeractions within the target and of a muon spectrometer

The OPERA experiment is described in detail in [35]and shown in Figure 19 Here we just point to the mainfeatures mostly in relation to the large ECC emulsion targetAt the occurrence of a neutrino interaction the resultingcharged particle tracks are detected by scintillator counterplanes placed behind each brick target wall similarly to whathappens in a sampling calorimeter There are about 150000ECC bricks in the detector target each weighing about 8 kgand consisting of a sandwich of 57 emulsion films and 56

lead plates (see Section 3) arranged into planes of about 10 times10m2 surface each Each target plane is followed by planes ofscintillator strips of identical cross-section readout by multi-anode photomultipliers

The event reconstruction procedure starts with signalsfrom the scintillators upon interaction of a neutrino from theCNGS beam On the average 20ndash30 neutrino interactions arecollected per day of CNGS operation Such interactions arenormally accompanied by a ldquoparticle showerrdquo that develops inthe calorimetric structure composed of brick and scintillatorplanes The reconstruction of the shower axis andor theidentification of a muon track allow (with a certain effi-ciency) identifying the brick where the neutrino interactionoccurred The candidate brick is then extracted from itstarget plane by a robot and the CS emulsions attached to itare removed and developed The brick is not unpacked andis stored underground waiting for a positive indication oftracks found in the CS (Figure 13) The CS is made of twoemulsion films for a total of 4 emulsion layers yielding up to4 microtracks A CS track is declared found if at least 3 outof the 4 microtracks are actually reconstructedThe scanningof the CS is the most time-consuming analysis procedureIt is performed in two large microscope laboratories locatedat LNGS and Nagoya with microscopes just dedicated to CSscanning Several tens of square centimeters are normallyscanned per each CS in order to look for neutrino-relatedtrack segments If no full tracks compatible with the eventreconstructed by the scintillators are found the brick isput back in the detector with a new CS Otherwise thebrick is exposed to cosmic-rays for a period of 12 hours toprovide the collection of a sufficient number of muon tracksfor the precise alignment of the brickrsquos films and for thecorrection of emulsion deformations After this the brick isfinally unpacked and all its films are developed in the large5 station facility at LNGS [35] Then the bricksrsquo emulsionfilms are shipped to the various scanning laboratories of thecollaboration for the vertex location analysis

Starting from the position and angle information ofthe CS track(s) the so-called scan back procedure initiatesby looking for CS track extrapolations to the brickrsquos filmsstarting from the most downstream ones Disappearanceof a scan-back track might indicate the presence of aninteraction vertex (Figure 2) In this case a general scanis performed around the disappeared track position overan equivalent brick volume of about 1 cm3 This procedurecalled decay search namely the identification of primaryneutrino vertices and of secondary vertices due to particledecays (eg that of a tau into one or more prongs) isconducted automatically and routinely by the nearly 40microscopes of theOPERAbrick scanning laboratoriesMoredetails on the event reconstruction in OPERA are given forexample in [68]

Once one or more vertices are found one can exploit allthe rich information stored in the emulsions for a MultipleCoulomb Scattering (MCS) analysis (for track momentumdetermination) or for the search of electron- or gamma-induced downstream showers Details on the track momen-tum determination by MCS can be found in [69] Theeffectiveness of these methods is illustrated in Figure 20


8Daughter

Side view

1

2

3

4

5

6

7

1205742

1205741

Figure 20 Display of the first OPERA event attributed to muon totau-neutrino oscillations The short tau track (red in the picture)decays into a daughter track likely a charged pion

which shows the display of the first tau candidate event foundby OPERA Several tracks are reconstructed originatingfrom the primary vertex One of those is found exhibitingthe peculiar kink topology indication of the productionand decay of a tau-lepton [70 71] This interpretation issupported by the detailed kinematical analysis of the eventassumed as the interaction of a tau-neutrino coming fromoscillation interacting in the lead plate of the selected brickand producing a tau in turn decaying into 120588 + ]

120591 finally

followed by the decay 120588 rarr 1205870 + 120587The OPERA experiment successfully completed in 2012

its data taking in theCNGS beam started in 2008 It exploiteda total neutrino flux produced by sim 18 times 1019 protons fromthe SPS hitting the neutrino production target The analysisof the events still ldquostoredrdquo in the bricks in the detector isin progress At the moment of writing several thousandneutrino interaction events have been located in the emulsionbricks So far 3]

120591candidate events have been identified with

an expected signal of 22 events for an estimated backgroundof 023 events This corresponds to a sim32120590 significance fora non-null observation of oscillations [72] The topologyof the second candidate event is compatible with that ofa tau-lepton decaying into three hadrons while the thirdevent announced very recently is a clean 120591 muonic decaycharacterized by a very low background Scanning of theremaining events will proceed until 2015 with the objective ofa stronger statistical confidence in the observation of ]

120583rarr

]120591oscillations A few more signal events are expected by the

completion of the analysisFurthermore given the capability of the experiment in

identifying prompt electrons through their characteristicelectromagnetic shower in the dense calorimeter constitutedby the ECC sandwich OPERA has recently provided lim-its to the observation of ]

120583rarr ]

119890oscillation Overall

19]119890interactions were observed in the event sample corre-

sponding to the 2008-2009 statistics out of which 6 satisfyingthe selection criteria for oscillated ]

119890 13 signal events were

expected with 94 events of background mainly due to thesim1 contamination of ]

119890of the ]

120583beam [73] This result is

very interesting because it provides so far the best upper

Figure 21 Display of a ]119890-induced event detected in the OPERA

target One of the prompt tracks initiates the characteristic electro-magnetic shower topology Note that the length of the shower shownin the picture is less than a couple of centimeters

limit for the exclusion of the low Δm2 parameter region ofthe so-called LSNDMiniBooNE signal possibly due to theexistence of a fourth and ldquosterilerdquo neutrino flavor The eventdisplay of an OPERA ]

119890-induced event is shown in Figure 21

7 The Future The Emulsion TechniqueBeyond Neutrino Oscillation Experiments

The vigorous RampD conducted for the OPERA experimentand the consequent dissemination of the modern emul-sion technique has led some of the groups participating inthe experiment to further continue this activity for futureapplications This strategy is also pursued by other groupsin Europe and Japan not previously involved in OPERASome of the applications concern fundamental physics whileothers refer to technological or even industrial applicationsIn [3] and references therein a few of the notable activi-ties are presented on experiments conducted with balloonairplane satellite and space station experiments for cosmic-ray physics or applications related to radiation dosimetryneutron flux measurement and monitoring imaging formedical applications and radiation biophysics As far asmore recent applications are concerned we can mention forexample the GRAINE balloon experiment for the study ofcosmic gamma-rays [74] a study on hadron fragmentationfor medical carbon therapy [75] and a development of aneutron camera for use in plasma physics experiments [76]

On the other hand the use of emulsion detectors andmodern (fast) scanning devices has caused a technologicalboost also in the active field of muon radiography The latterwas originally proposed long ago for the measurement of thethickness of mountains [77] and for the search for unknownburial cavities in pyramids [78] The technique is based onthe fact that the interaction of primary cosmic-rays withthe atmosphere provides a stable source of muons that canbe employed for various applications of muon radiography


(a) (b)

Figure 22 Phantoms used for the test measurement on emulsion-based proton radiography (a) ldquosteprdquo phantom (b) ldquorodrdquo phantom 45 cmthick containing five 5 times 5mm2 aluminum rods positioned at different depths in a PMMA structure

and in particular for the study of the internal structure ofvolcanoes This application pioneered in Japan [79ndash82] hasrecently led to very interesting results and opened the wayto unexpected applications Related applications of muonradiography are in fact in the field of the investigation ofgeological structures such as glacier bedrocks and in thesearch for ice concentrations in Alpine mountains as well asin the inspection of the interior of building structures andblast furnaces In these cases emulsion films represent a veryappropriate detector option for twomain reasons the unbeat-able position and angular resolutions in the measurementof the muon track (less than 1 120583m and a few mrad resp)and the passive nature of the device not requiring electricpower electronics radio transmission of data and so forthHowever a rather long exposure time might be required (upto severalmonths) for any realistic detector surface and quasireal-time analysis of the emulsion data poses challengingrequirements due to the time needed to analyze emulsions byoptical microscopesThe technique will definitely profit fromthe advances in the realization of suitable emulsion films and(mainly) from the availability of more and more performingscanning microscopes More information can be found in[83]

A notable recent application of the emulsion techniqueis in the framework of proton radiography for medicaldiagnostics A newmethod based on emulsion film detectorswas proposed and tested in Bern and PSI [84] This is atechnique in which images are obtained by measuring theposition and the residual range of protons passing throughthe patientrsquos body For this purpose nuclear emulsion filmsinterleaved with tissue-equivalent absorbers can be used toreconstruct proton tracks with very high accuracy Protonradiography can be applied to proton therapy in order toobtain direct information on the average tissue density fortreatment planning optimization and to perform imagingwith very low dose to the patient

The detector used in [84] was coupled to two phantomsshown in Figure 22 The detection apparatus is divided intotwo parts The first one is made of 30 OPERA-like emulsionfilms each interleaved with 3 polystyrene absorber platesallowing tracking of passing-through protons using a mini-mal number of filmsThe secondpart is composed of 40 films

Rang

e (m

m)

74

72

70

68

66

64

5060

70

X(m

m)

Y (mm)20304050607080

Figure 23 Measured proton range as a function of the transversecoordinates yielding a proton radiography image of the ldquorodrdquophantom shown in Figure 21

each interleavedwith one polystyrene plate allowing a precisemeasurement of the proton range in correspondence of theBragg peak The overall dimensions of the detector are 102times 125 cm2 in the transverse direction and 903mm along thebeam The results of an exposure to 138MeV protons of thedetector placed behind the ldquorodrdquo phantom (Figure 22) areshown in Figure 23 Also for this application the techniquewill become more and more appealing with the furtherprogress in the high-speed analysis of emulsion films

Another notable field of application of emulsion detectorshas been originally proposed by the Nagoya group for thedetection of the Dark Matter of the Universe [85] WeaklyInteractingMassive Particles (WIMPs) possible DarkMattercandidates could be in fact detected by measuring the slownuclear recoil after their interaction with massive high-density emulsion targets In the case of a WIMP with a massof about 100GeV hitting an Ag nucleus in the emulsiongel one would obtain a recoil momentum of sim100 keV witha corresponding range of only 100 nm In order to detectsuch a short heavily ionizing track the Nagoya group ispresently studying the technical feasibility of the so-calledNanoimaging Tracking (NIT) [86ndash88] The first requirementis to go from the 200 nm AgBr crystal size of the presentOPERA emulsion gel to about 40 nm size This would


(a) (b)

Figure 24 Tracks from minimum ionizing particles and from heavily ionizing nuclear fragments from the annihilation vertex of anantiproton observed in the standard gel (a) and in the newly developed gel (b) for the AEgIS experiment

correspond to a density of more than 10 AgBr crystals permicron In addition in order to have a sufficiently longtrack the idea is to apply the so-called emulsion swellingprior to development to expand the 100 nm long recoiltracks up to 1000 nm or more First tests are encouragingInternal radioactivity and fog grains making random trackcoincidences constitute the main background

Still on fundamental science applications emulsion filmscan be used as high-precision tracker devices to determinethe antihydrogen annihilation vertices with micrometricspace resolution or even as targets by directly observingantimatter annihilation vertices This is a recent applicationconsidered by the Bern group [89] for the AEgIS experimentat CERN [90] In AEgIS the free-fall of antihydrogen atomslaunched horizontally will be measured to directly determinefor the first time the gravitational acceleration of neutralantimatter by matter The vertical precision on the measuredannihilation point will be around 1120583m RMS This will beachieved by adding an emulsion detector to the originallyforeseen 120583-strip detector For the first time nuclear emulsionfilms will be used in vacuum at relatively low temperatureAn intense RampD program on emulsion films has beenstarted to cope with their operation under such conditionsFirst results on the behavior of emulsions in vacuum havealready been published [89] Results were also achieved withantiprotons annihilating in emulsions in vacuum and at roomtemperature [91]

For AEgIS new emulsion gels with higher sensitivityare being considered to increase the detection efficiencyusing glass instead of plastic as base material Glass in factis better suited to achieve the highest position resolutionsthanks to its superior environmental stability (temperatureand humidity) as compared to plastic bases Emulsions of thenew type weremanufactured in Bernwith gel provided by theUniversity of Nagoya Antiproton interactions reconstructedwithin the conventional (OPERA-like) and new gel are shownin Figure 24 One can definitely see the better features ofthe new gel in terms of sensitivity to nuclear fragments andnoise The new gel composition can be tuned for exampleto provide higher detection efficiency to fragments fromantimatter annihilation rather than to MIP contrary to whatwas done for instance in OPERA

References

[1] P H Fowler D H Perkins and C F Powell The Study ofElementary Particles By the Photographic Method PergamonPress 1959

[2] W H BarkasNuclear Research Emulsion Academic Press NewYork NY USA 1973

[3] G De Lellis A Ereditato and K Niwa Nuclear EmulsionsDetectors For Particles and Radiation vol 21 Landolt-Bornstein- Nuclei and Atoms 2011 Edited by C W Fabjan H Schopper

[4] S Kinoshita ldquoThe photographic action of the 120572-particlesemitted from radio-active substancesrdquo Proceedings of the RoyalSociety A vol 83 pp 432ndash453 1910

[5] C F Powell G P S Occhialini D L Livesey and L V ChiltonldquoA new photographic emulsion for the detection of fast chargedparticlesrdquo Journal of Scientific Instruments vol 23 no 5 article304 pp 102ndash106 1946

[6] C M G Lattes H Muirhead G P S Occhialini and C FPowell ldquoProcesses involving charged mesonsrdquo Nature vol 159no 4047 pp 694ndash697 1947

[7] M F Kaplon B Peters H L Reynolds and D M Ritson ldquoTheenergy spectrum of primary cosmic radiationrdquo Physical Reviewvol 85 no 2 pp 295ndash309 1952

[8] J Nishimura SoryushironKenkyu vol 12 p 24 1956[9] CMG LattesM SMMantovani C Santos et al ldquoCHACAL-

TAYA emulsion chamber experimentrdquo Progress of TheoreticalPhysics vol 47 pp 1ndash125 1971

[10] I Ohta K Kasahara I Mito A Ohsawa T Taira and S ToriiProceedings of theInternational Cosmic Ray Conference vol 3 p2250 1973

[11] M Akashi et al Proceedings of the InternationalCosmic RayConference vol 7 p 2549 1975

[12] A V Apanasenko V A Sukhadolskaya V A Derbinab et alldquoComposition and energy spectra of cosmic-ray primaries inthe energy range 1013-1015 eVparticle observed by Japanese-Russian joint balloon experimentrdquo Astroparticle Physics vol 16no 1 pp 13ndash46 2001

[13] K Niu E Mikumo and Y Maeda ldquoA possible decay in flight ofa new type particlerdquo Progress of Theoretical Physics vol 46 no5 p 1644 1971

[14] N Ushida T Kondo G Fujioka et al ldquoExperimental details onlifetimemeasurements of neutrino-produced charmedparticlesin a tagged emulsion spectrometerrdquo Nuclear Instruments andMethods in Physics Research vol 224 no 1-2 pp 50ndash64 1984


[15] E H S Burhop D H Davis D N Tovee et al ldquoObservationof a likely example of the decay of a charmed particle producedin a high energy neutrino interactionrdquo Physics Letters B vol 65no 3 pp 299ndash304 1976

[16] D Allasia C Angelini P Bagnaia et al ldquoInvestigation of thedecay of charmed particles produced in neutrino interactionsrdquoNuclear Physics B vol 176 no 1 pp 13ndash36 1980

[17] N Ushida T Kondob S Tasaka et al ldquoProduction charac-teristics of charmed particles in neutrino interactionsrdquo PhysicsLetters B vol 206 no 2 pp 380ndash384 1988

[18] N Ushida T Kondo G Fujioka et al ldquoMeasurement of thelifetimerdquo Physical Review Letters vol 45 no 13 pp 1049ndash10521980

[19] N Ushida T Kondo G Fujioka et al ldquoMeasurement of119863+ 119865+and Λ

119888

+ charmed-particle lifetimesrdquo Physical Review Lettersvol 45 no 13 pp 1053ndash1056 1980

[20] N Ushida T Kondo G Fujioka et al ldquoNew result for thelifetime of the D0 mesonrdquo Physical Review Letters vol 48 no13 pp 844ndash847 1982

[21] N Ushida et al ldquoLifetimes of the charmed particles119863plusmn 119865plusmn andΛ119888

+ produced by neutrinosrdquo Physical Review Letters vol 56 no17 pp 1767ndash1770 1986

[22] N Ushida T Kondob S Tasaka et al ldquoCross sections forneutrino production of charmed particlesrdquo Physics Letters Bvol 206 no 2 pp 375ndash379 1988

[23] N Ushida T Kondo G Fujioka et al ldquoUpper limits to V120583minus]120591

oscillation and ]120583minus 120591 couplingrdquo Physical Review Letters vol 47

no 24 pp 1694ndash1697 1981[24] N Ushida et al ldquoLimits to V

120583V119890rarr V120591oscillations and V

120583V119890rarr

120591minus direct couplingrdquo Physical Review Letters vol 57 no 23 pp2897ndash2900 1986

[25] S Aoki R Arnold G Baroni et al ldquoA hybrid experiment tosearch for beauty particlesrdquo Nuclear Instruments and Methodsin Physics Research Section A vol 274 no 1-2 pp 64ndash78 1989

[26] K Kodama N Ushida R L Lander et al ldquoHybrid emulsionspectrometer for the detection of hadronically produced heavyflavor statesrdquo Nuclear Instruments and Methods in PhysicsResearch Section A vol 289 no 1-2 pp 146ndash167 1990

[27] J Beringer J -F Arguin and R M Barnett ldquoThe review ofparticle physicsrdquo Physical Review vol 86 2012

[28] E Eskut et al ldquoThe CHORUS experiment to search for V120583rarr

V120591oscillationrdquo Nuclear Instruments and Methods in Physics

Research Section A vol 401 no 1 pp 7ndash44 1997[29] S Aoki et al ldquoNuclear emulsions in a large hybrid experiment

(CHORUS) to search for V120583rarr V

120591oscillationsrdquo Nuclear

Instruments andMethods in Physics Research Section A vol 447no 3 pp 361ndash376 2000

[30] K Hoshino and G Rosa ldquoA facility at CERN for pouringthe photographic emulsions for nuclear and particle researchrdquoInternational Journal of Radiation Applications and Instrumen-tation vol 12 no 1ndash6 pp 477ndash481 1986

[31] A Ereditato K Niwa and P Strolin ldquoThe emulsion techniquefor short medium and long baseline V

120583minus V119879

oscillationexperimentsrdquo Tech Rep INFNAE-9706 Nagoya DPNU-97-07 1997

[32] A Ereditato K Niwa and P Strolin ldquoOPERA an emulsiondetector for a long baselin V

120583minus V119879oscillation searchrdquo Nuclear

Physics B vol 66 no 1ndash3 pp 423ndash427 1998[33] K Niwa ldquoContrib to the Snowmassrdquo in 94 Conference on

particle and Nuclear Astrophysics and Cosmology in the nextMillennium Snowmass 1994

[34] T Nakamura A Arigaa T Ban et al ldquoThe OPERA film newnuclear emulsion for large-scale high-precision experimentsrdquoNuclear Instruments and Methods in Physics Research Section Avol 556 no 1 pp 80ndash86 2006

[35] R Acquafredda T Adam N Agafonova et al ldquoThe OPERAexperiment in the CERN to Gran Sasso neutrino beamrdquo Journalof Instrumentation vol 4 2009

[36] K Niwa K Hoshino and K Niu in Proceedings of the Interna-tional Cosmic Ray Symposium on High Energy Phenomena vol149 Cosmic Ray Laboratory University of Tokyo 1974

[37] T Nakano [PhD thesis] University of Nagoya 1997[38] T Nakano Butsuri vol 56 p 411 2001[39] K Kodama N Saoulidou G Tzanakos et al ldquoDetection and

analysis of tau-neutrino interactions in DONUT emulsiontargetrdquo Nuclear Instruments and Methods in Physics ResearchSection A vol 493 no 1-2 pp 45ndash66 2002

[40] M De Serio M Ievaa M T Muciaccia et al ldquoHigh precisionmeasurements with nuclear emulsions using fast automatedmicroscopesrdquo Nuclear Instruments and Methods in PhysicsResearch Section A vol 554 no 1ndash3 pp 247ndash254 2005

[41] M De Serio M Ievaa S Simone et al ldquoMomentum measure-ment by the angular method in the Emulsion Cloud ChamberrdquoNuclear Instruments and Methods in Physics Research Section Avol 512 no 3 pp 539ndash545 2003

[42] K Kodama N Saoulidou G Tzanakos et al ldquoMomentummea-surement of secondary particle by multiple coulomb scatteringwith emulsion cloud chamber in DONuT experimentrdquo NuclearInstruments andMethods in Physics Research Section A vol 574no 1 pp 192ndash198 2007

[43] K Kodama K Hoshino M Komatsu et al ldquoStudy of electronidentification in a few GeV region by an emulsion cloudchamberrdquo Review of Scientific Instruments vol 74 no 1 p 532003

[44] L Arrabito D Autiero C Bozza et al ldquoElectronpion sepa-ration with an Emulsion Cloud Chamber by using a NeuralNetworkrdquo Journal of Instrumentation vol 2 2007

[45] T Nakano Journal of TheSociety of Photographic Science andTechnology vol 71 no 4 p 229 2008

[46] I Kreslo M Cozzi A Ereditato et al ldquoHigh-speed analysis ofnuclear emulsion films with the use of dry objective lensesrdquoJournal of Instrumentation vol 3 2008

[47] G Rosa A Di Bartolomeo G Grella and G RomanoldquoAutomatic analysis of digitized TV-images by a computer-driven optical microscoperdquo Nuclear Instruments and Methodsin Physics Research A vol 394 no 3 pp 357ndash367 1997

[48] N Armenise M De Serioa M Ieva et al ldquoHigh-speed particletracking in nuclear emulsion by last-generation automaticmicroscopesrdquo Nuclear Instruments and Methods in PhysicsResearch Section A vol 551 no 2-3 pp 261ndash270 2005

[49] L Arrabito E Barbutob C Bozza et al ldquoHardware per-formance of a scanning system for high speed analysis ofnuclear emulsionsrdquoNuclear Instruments andMethods in PhysicsResearch Section A vol 568 no 2 pp 578ndash587 2006

[50] L Arrabito C Bozza S Buontempo et al ldquoTrack reconstruc-tion in the emulsion-lead target of the OPERA experimentusing the ESS microscoperdquo Journal of Instrumentation vol 22007

[51] A Ariga ldquoRecent emulsion technologiesrdquo AIP Conference Pro-ceedings vol 1382 pp 253ndash255

[52] T Fukuda S Fukunaga H Ishida et al ldquoTime-dependentdensity functional theory and the real-time dynamics of fermisuperfluidsrdquo Nuclear Theory vol 63 49 pages 2013


[53] B Pontecorvo Journal of Experimental andTheoretical Physicsvol 6 p 429 1957

[54] B Pontecorvo Journal of Experimentaland Theoretical Physicsvol 7 p 172 1958

[55] Z Maki M Nakagawa and S Sakata ldquoRemarks on the unifiedmodel of elementary particlesrdquo Progress of Theoretical Physicsvol 28 no 5 pp 870ndash880 1962

[56] E Eskut A Kayis-Topaksu G Onengut et al ldquoFinal resultson V120583minus V119879oscillation from the CHORUS experimentrdquo Nuclear

Physics B vol 793 no 1-2 pp 326ndash343 2008[57] GOnengut R vanDantzigM de Jong et al ldquoMeasurements of

D-zero production and branching fractions in neutrino nucleonscatteringrdquo Physics Letters B vol 613 p 105 2004

[58] A Kayis-Topaksu G Onengut R van Dantzig et al ldquoAssoci-ated charm production in neutrino-nucleus interactionsrdquo TheEuropean Physical Journal C vol 52 no 3 pp 543ndash552 2007

[59] A Kayis-Topaksu G Onengut et al ldquoObservation of one eventwith the characteristics of associated charm production inneutrino charged-current interactionsrdquo Physics Letters B vol539 no 3-4 pp 188ndash196 2002

[60] A Ereditato P Strolin and G Romano ldquoStudy of a newexperiment for the search of V

120583minusV120591oscillationsrdquoNuclear Physics

B vol 54 no 3 pp 139ndash150 1997[61] A S Ayan et al CERN-SPSC97-5 SPSCI213 1997[62] K S Hirata T Kajita M Koshiba et al ldquoExperimental study of

the atmospheric neutrino fluxrdquo Physics Letters B vol 205 no2-3 pp 416ndash420 1988

[63] Y Fukuda T Hayakawa E Ichihara et al ldquoEvidence foroscillation of atmospheric neutrinosrdquo Physical Review Lettersvol 81 no 8 pp 1562ndash1567 1998

[64] K Kodama N Saoulidoub G Tzanakos et al ldquoDetectionand analysis of tau-neutrino interactions in DONUT emulsiontargetrdquo Nuclear Instruments and Methods in Physics ResearchSection A vol 493 no 1-2 pp 45ndash66 2002

[65] K Kodama C Andreopoulosb N Giokaris et al ldquoIdentifica-tion of neutrino interactions using the DONUT spectrometerrdquoNuclear Instruments and Methods in Physics Research Section Avol 516 no 1 pp 21ndash33 2004

[66] K Kodama N Ushidaa C Andreopoulos et al ldquoObservationof tau neutrino interactionsrdquo Physics Letters B vol 504 no 3pp 218ndash224 2001

[67] K Kodama N Ushida C Andreopoulos et al ldquoFinal tau-neutrino results from the DONuT experimentrdquo Physical ReviewD vol 78 no 5 37 pages 2008

[68] N Agafonova A Anokhina S Aoki et al ldquoThe detection ofneutrino interactions in the emulsionlead target of the OPERAexperimentrdquo Journal of Instrumentation vol 4 2009

[69] N Agafonova A Alexander and O Altinok ldquoMomentummeasurement by the multiple Coulomb scattering method inthe OPERA lead-emulsion targetrdquo New Journal of Physics vol14 Article ID 013026 2012

[70] N Agafonova A Aleksandrov O Altinok et al ldquoObservationof a first V

120591candidate event in the OPERA experiment in the

CNGS beamrdquo Physics Letters B vol 691 no 3 pp 138ndash145 2010[71] A Ereditato Il NuovoSaggiatore vol 26 no 3-4 p 5 2010[72] A Pastore ldquoOPERA Collaborationrdquo in Proceeding of the Inter-

national Europhysics Conference on High Energy Physics pp 18ndash24 Stockholm Sweden July 2013

[73] N Agafonova A Aleksandrov A Anokhina et al ldquoAddendumsearch for V

120583rarr V119890oscillations with the OPERA experiment in

the CNGS beamrdquo Journal of High Energy Physics vol 07 p 0042013

[74] S Takahashi et al in Proceedings of the 33International CosmicRay Conference Rio de Janeiro 2013

[75] G De Lellis S Buontempo F Di Capua et al ldquoMeasurementof the fragmentation of Carbon nuclei used in hadron-therapyrdquoNuclear Physics A vol 853 no 1 pp 124ndash134 2011

[76] H Tomita G Kawamura Z Huang et al ldquoSecondary electronemission from a negatively charged spherical dust particle byelectron incidencerdquo Plasma and Fusion Research vol 8 2013

[77] E P Georg Commonwealth of England 1955[78] L W Alvarez J A Anderson F El Bedwei et al ldquoSearch for

hidden chambers in the pyramidsrdquo Science vol 167 no 3919pp 832ndash839 1970

[79] K Nagamine M Iwasakia K Shimomura et al ldquoMethodof probing inner-structure of geophysical substance with thehorizontal cosmic-ray muons and possible application to vol-canic eruption predictionrdquoNuclear Instruments andMethods inPhysics Research Section A vol 356 no 2-3 pp 585ndash595 1995

[80] H K M Tanaka K Nagaminea N Kawamura et al ldquoDevel-opment of a two-fold segmented detection system for nearhorizontally cosmic-ray muons to probe the internal structureof a volcanordquo Nuclear Instruments and Methods in PhysicsResearch Section A vol 507 no 3 pp 657ndash669 2003

[81] H K M Tanaka K Nagaminea S N Nakamura et alldquoRadiographic measurements of the internal structure of MtWest Iwate with near-horizontal cosmic-ray muons and futuredevelopmentsrdquo Nuclear Instruments and Methods in PhysicsResearch Section A vol 555 no 1-2 pp 164ndash172 2005

[82] HKMTanaka TNakano S Takahashi et al ldquoHigh resolutionimaging in the inhomogeneous crust with cosmic-ray muonradiography the density structure below the volcanic craterfloor of Mt Asama Japanrdquo Earth and Planetary Science Lettersvol 263 no 1-2 pp 104ndash113 2007

[83] International Conference onMuon and Neutrino Radiographyhttpmnt2012in2p3frpage id=23

[84] S Braccini A Ereditato I Kreslo et al ldquoFirst results onproton radiography with nuclear emulsion detectorsrdquo Journalof Instrumentation vol 5 no 9 Article ID P09001 2010

[85] T Naka M Kimura M Nakamura et al ldquoRampD status ofnuclear emulsion for directional dark matter searchrdquo HighEnergy Physics 2011

[86] MNatsumeKHoshinoaKKuwabara et al ldquoLow-velocity iontracks in fine grain emulsionrdquoNuclear Instruments andMethodsin Physics Research Section A vol 575 no 3 pp 439ndash443 2007

[87] T Naka M Natsume and K Niwa ldquoDevelopment of emulsiontrack expansion techniques for optical-microscopy-observationof low-velocity ion tracks with ranges beyond optical resolutionlimitrdquo Nuclear Instruments and Methods in Physics ResearchSection A vol 581 no 3 pp 761ndash76 2007

[88] T Naka 2008 invited talk at the III International Workshop onNuclear Emulsion Techniques Nagoya

[89] C Amsler A Ariga T Ariga et al ldquoA new application ofemulsions to measure the gravitational force on antihydrogenrdquoJournal of Instrumentation vol 8 2013

[90] G Dobrychev et al ldquoAEgIS Proposalrdquo 2007 CERN-SPSC-P-334

[91] M Kimura S Aghionb O Ahlen et al ldquoDevelopment ofnuclear emulsions with 1120583m spatial resolution for the AEgISexperimentrdquo Nuclear Instruments and Methods in PhysicsResearch Section A vol 732 pp 325ndash329 2013

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


FluidsJournal of

Atomic and Molecular Physics

Journal of



Advances in Condensed Matter Physics

OpticsInternational Journal of



AstronomyAdvances in

International Journal of


Superconductivity


Statistical MechanicsInternational Journal of


GravityJournal of


AstrophysicsJournal of


Physics Research International


Solid State PhysicsJournal of

Computational Methods in Physics

Journal of



Soft MatterJournal of

Hindawi Publishing Corporationhttpwwwhindawicom

AerodynamicsJournal of

Volume 2014


PhotonicsJournal of


Journal of

Biophysics


ThermodynamicsJournal of


for several reasons for the higher content of silver halide(by about one order of magnitude) for the larger thickness(sim times100) and for the smaller size and more uniform silvergrains

Several quantities characterize nuclear emulsions as aparticle detector At first their sensitivity related to thenumber of grains that are produced for a given energy releaseby an incoming particle The second feature is the so-calledfadingThis is the oxidation process that causes the reductionof the number of ldquostoredrdquo grains along the track as a functionof time High relative humidity and temperature could accel-erate fading leading to the loss of detectable tracks As wewill see fading was exploited for recent applications in orderto ldquocleanrdquo emulsions prior to their use erasing unwantedaccumulated cosmic-ray and environmental radiation tracksThe third factor is the mechanical distortion of the emulsionlayersThis occurs either locally or globally and can obviouslyaffect the knowledge of the absolute position of particletracks and more seriously their direction and curvatureHowever several effective techniques exist and are routinelyemployed to reduce distortions and their effects Finallyrandom distributed grains (the so-called ldquofogrdquo) producedby thermal excitation constitute a background for trackrecognition in the emulsion This potential background fortrack identification and reconstruction is usually quantifiedby the number of (fog) grains present per 1000 120583m3 Figure 1shows an electron microscope image of the silver crystals inthe emulsion gel and the reconstructed image of a minimumionizing particle track (MIP) The sensitivity corresponds toabout 30 grains100120583m

2 A Brief History

Emulsions have a long history The first use of the detectordates to the pioneering work of Kinoshita [4] and later onby Powell et al [5] who got important results in the 1950rsquosby profiting from the continuous progress in the productionof gel with improved quality The discovery of the pion in1947 constituted an outstanding success of the technique[6] An important breakthrough was represented by theinvention of the so-called Emulsion Cloud Chamber (ECC)(Figure 2) In the ECC emulsion films or thicker plates areinterspaced by passive material layers made of plastic ormetal constituting what we would call today a sampling-calorimeter In this way one can potentially fully reconstructall tracks of an electromagnetic or hadronic shower With theECC arrangement emulsions became high space-resolutiontracking devices with full 3D reconstruction capabilities inaddition to the ldquostandardrdquo use as a pure volumeimagingdetector Similar sandwich arrangements were proposed evenbefore the advent of the ECC technique as reported in [2]

The study of events taken with ECC detectors profitsfrom the potential reconstruction of all tracks producedin a primary interaction occurring in the passive materialSpace angles are measured for track segments and showerenergy and axis reconstruction is performed as well Particledecays can be identified by detecting kinks in the tracksMoreover by exploiting Multiple Coulomb Scattering andemulsion ionization measurements one can obtain accurate

measurements of the particle momenta In the early timesthe mechanical stability of the ECC sandwich was generallyensured by a vacuum packing paper known as ldquoorigamirdquoalso needed to protect the films from the external lighthumidity and polluting gases Film-to-film alignment can beperformed by suitable X-ray exposure As we will see lateron with the OPERA experiment the ECC technique reachedits highest development with several insights and innovativetechnological solutions

The ECC was first developed and used by Kaplon tostudy heavy primaries in cosmic-ray interactions [7] ECCdetectors were then applied to the study of the cosmic-rayspectrum and to very high energy interaction processesNishimura who contributed significantly to the developmentof the technique proposed the ECC for the measurementof the energy of 120574-rays through the study of the inducedelectromagnetic shower and proposed the method of tuningthe development of electron showers by a suitable use ofpassive material plates [8] Still in Japan and in collaborationwith the FUJI companyNiu proposed double-sided emulsionplates where the sensitive emulsion is deposited on either sideof a plastic base [3] The optical properties of the base werechosen to be close to those of the emulsion gel (meta-acryliclucite) The use of a plastic base between the two emulsionlayers allows the precise measurement of the incident particletrack angle by connecting grains near the base which are notaffected by distortions (Figure 3)

With ECC detectors the emulsion technique got animpressive boost due to the possibility of realizing largesize (surface and volume) detectors specially for cosmic-raydetection thanks to the use of dense metal plates comple-menting the outstanding tracking properties of the emulsionlayers One canmention in particular the Chacaltaya [9] andtheMt Fuji [10 11] experiments and inmore recent times theRUNJOB [12] and JACEE [12] detectors

Thanks to an experiment conducted with an ECC detec-tor placed on a cargo flight in 1971 Niu et al discoveredthe so-called X-particles [13] by observing a cosmic-rayinduced event where two charged particles produced in aprimary interaction exhibit a clearly identified kink decay-topology (Figure 4) Today we know that that event had tobe attributed to charmed meson production and decay Thishappened three years before the discovery of the 119869Ψ particleby the groups of Richter and Ting with electronic detectors ataccelerators More information on Niursquos results can be foundin [3] and references therein

With the advent of the electronic particle detectors onestarted using ECCs in conjunction with electronic deviceswith the main purpose of giving to some extent time-resolution to the emulsions through proper association oftracks reconstructed ldquoat the same timerdquo in both detectorsalthough with a different spatial resolution We talk in thiscase of a hybrid experimental setup Thanks to the electronicdetectors tracks originated by particles interacting in theECC are preselected to approximately identify the positionwhere to start the emulsion scanning or look for interactionvertices as shown in Figure 2 The consequent emulsionscanning allows accurately measuring and studying theevents with much higher space accuracy (see eg [14])


(a)

100120583

m

(b)



Emulsion Lead ECCCS


film plate








Base-track














40

35

30

25

20

15

10

9

0 0

138 cm

350 cm

B B

D (C)(C)

(B)(B) AA D1205870

1205870

Plat

e num

ber

10120583m

B998400 B998400C998400 C998400


(a)

A

B

D

1205870

C

B998400

C998400

10 120583m

Z projection

(b)


102mm

128mm

79mm

ECCbrick

264mm





Emulsion layer






(a) (b)











GD 303FD 101

Nagoya gel

GD 477FD 19

Russian gel

GD 330FD 5410

0120583

m


Scan

ning

spee

d (c

m2h

)

100

10

11

01

001

0001

0003

0082

72









(a) (b)



5 CHORUS and DONUT


119890 ]120583and ]

120591) can


1 1198982and 119898



13= 1198982

3minus 11989821and








Interaction

Decay

120591

120591

120583












Beam

Anticounter

ShieldingFibre

trackers


Hexagonalmagnet


H ST

Spectrometer

120583

TV

sim15m















119888















am ax

is (120583

m)

800

700

600

500

400

300

200

100

0


Emulsionlayer

Emulsionlayer

Acetate base











120583rarr




120583rarr





Pb Emulsion layers


ECC brick

Electronicstrackers

120591

120591

1mm











8Daughter

Side view

1

2

3

4

5

6

7

1205742

1205741



120591 finally





120583rarr




120583rarr ]






119890of the ]











(a) (b)





Rang

e (m

m)

74

72

70

68

66

64

5060

70

X(m

m)

Y (mm)20304050607080





(a) (b)





References





















119888










120583V119890rarr













120583minus V119879










































































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




(a)

100120583

m

(b)



Emulsion Lead ECCCS


film plate








Base-track














40

35

30

25

20

15

10

9

0 0

138 cm

350 cm

B B

D (C)(C)

(B)(B) AA D1205870

1205870

Plat

e num

ber

10120583m

B998400 B998400C998400 C998400


(a)

A

B

D

1205870

C

B998400

C998400

10 120583m

Z projection

(b)


102mm

128mm

79mm

ECCbrick

264mm





Emulsion layer






(a) (b)











GD 303FD 101

Nagoya gel

GD 477FD 19

Russian gel

GD 330FD 5410

0120583

m


Scan

ning

spee

d (c

m2h

)

100

10

11

01

001

0001

0003

0082

72









(a) (b)



5 CHORUS and DONUT


119890 ]120583and ]

120591) can


1 1198982and 119898



13= 1198982

3minus 11989821and








Interaction

Decay

120591

120591

120583












Beam

Anticounter

ShieldingFibre

trackers


Hexagonalmagnet


H ST

Spectrometer

120583

TV

sim15m















119888















am ax

is (120583

m)

800

700

600

500

400

300

200

100

0


Emulsionlayer

Emulsionlayer

Acetate base











120583rarr




120583rarr





Pb Emulsion layers


ECC brick

Electronicstrackers

120591

120591

1mm











8Daughter

Side view

1

2

3

4

5

6

7

1205742

1205741



120591 finally





120583rarr




120583rarr ]






119890of the ]











(a) (b)





Rang

e (m

m)

74

72

70

68

66

64

5060

70

X(m

m)

Y (mm)20304050607080





(a) (b)





References





















119888










120583V119890rarr













120583minus V119879










































































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics





Base-track














40

35

30

25

20

15

10

9

0 0

138 cm

350 cm

B B

D (C)(C)

(B)(B) AA D1205870

1205870

Plat

e num

ber

10120583m

B998400 B998400C998400 C998400


(a)

A

B

D

1205870

C

B998400

C998400

10 120583m

Z projection

(b)


102mm

128mm

79mm

ECCbrick

264mm





Emulsion layer






(a) (b)











GD 303FD 101

Nagoya gel

GD 477FD 19

Russian gel

GD 330FD 5410

0120583

m


Scan

ning

spee

d (c

m2h

)

100

10

11

01

001

0001

0003

0082

72









(a) (b)



5 CHORUS and DONUT


119890 ]120583and ]

120591) can


1 1198982and 119898



13= 1198982

3minus 11989821and








Interaction

Decay

120591

120591

120583












Beam

Anticounter

ShieldingFibre

trackers


Hexagonalmagnet


H ST

Spectrometer

120583

TV

sim15m















119888















am ax

is (120583

m)

800

700

600

500

400

300

200

100

0


Emulsionlayer

Emulsionlayer

Acetate base











120583rarr




120583rarr





Pb Emulsion layers


ECC brick

Electronicstrackers

120591

120591

1mm











8Daughter

Side view

1

2

3

4

5

6

7

1205742

1205741



120591 finally





120583rarr




120583rarr ]






119890of the ]











(a) (b)





Rang

e (m

m)

74

72

70

68

66

64

5060

70

X(m

m)

Y (mm)20304050607080





(a) (b)





References





















119888










120583V119890rarr













120583minus V119879










































































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




40

35

30

25

20

15

10

9

0 0

138 cm

350 cm

B B

D (C)(C)

(B)(B) AA D1205870

1205870

Plat

e num

ber

10120583m

B998400 B998400C998400 C998400


(a)

A

B

D

1205870

C

B998400

C998400

10 120583m

Z projection

(b)


102mm

128mm

79mm

ECCbrick

264mm





Emulsion layer






(a) (b)











GD 303FD 101

Nagoya gel

GD 477FD 19

Russian gel

GD 330FD 5410

0120583

m


Scan

ning

spee

d (c

m2h

)

100

10

11

01

001

0001

0003

0082

72









(a) (b)



5 CHORUS and DONUT


119890 ]120583and ]

120591) can


1 1198982and 119898



13= 1198982

3minus 11989821and








Interaction

Decay

120591

120591

120583












Beam

Anticounter

ShieldingFibre

trackers


Hexagonalmagnet


H ST

Spectrometer

120583

TV

sim15m















119888















am ax

is (120583

m)

800

700

600

500

400

300

200

100

0


Emulsionlayer

Emulsionlayer

Acetate base











120583rarr




120583rarr





Pb Emulsion layers


ECC brick

Electronicstrackers

120591

120591

1mm











8Daughter

Side view

1

2

3

4

5

6

7

1205742

1205741



120591 finally





120583rarr




120583rarr ]






119890of the ]











(a) (b)





Rang

e (m

m)

74

72

70

68

66

64

5060

70

X(m

m)

Y (mm)20304050607080





(a) (b)





References





















119888










120583V119890rarr













120583minus V119879










































































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




(a) (b)











GD 303FD 101

Nagoya gel

GD 477FD 19

Russian gel

GD 330FD 5410

0120583

m


Scan

ning

spee

d (c

m2h

)

100

10

11

01

001

0001

0003

0082

72









(a) (b)



5 CHORUS and DONUT


119890 ]120583and ]

120591) can


1 1198982and 119898



13= 1198982

3minus 11989821and








Interaction

Decay

120591

120591

120583












Beam

Anticounter

ShieldingFibre

trackers


Hexagonalmagnet


H ST

Spectrometer

120583

TV

sim15m















119888















am ax

is (120583

m)

800

700

600

500

400

300

200

100

0


Emulsionlayer

Emulsionlayer

Acetate base











120583rarr




120583rarr





Pb Emulsion layers


ECC brick

Electronicstrackers

120591

120591

1mm











8Daughter

Side view

1

2

3

4

5

6

7

1205742

1205741



120591 finally





120583rarr




120583rarr ]






119890of the ]











(a) (b)





Rang

e (m

m)

74

72

70

68

66

64

5060

70

X(m

m)

Y (mm)20304050607080





(a) (b)





References





















119888










120583V119890rarr













120583minus V119879










































































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics





GD 303FD 101

Nagoya gel

GD 477FD 19

Russian gel

GD 330FD 5410

0120583

m


Scan

ning

spee

d (c

m2h

)

100

10

11

01

001

0001

0003

0082

72









(a) (b)



5 CHORUS and DONUT


119890 ]120583and ]

120591) can


1 1198982and 119898



13= 1198982

3minus 11989821and








Interaction

Decay

120591

120591

120583












Beam

Anticounter

ShieldingFibre

trackers


Hexagonalmagnet


H ST

Spectrometer

120583

TV

sim15m















119888















am ax

is (120583

m)

800

700

600

500

400

300

200

100

0


Emulsionlayer

Emulsionlayer

Acetate base











120583rarr




120583rarr





Pb Emulsion layers


ECC brick

Electronicstrackers

120591

120591

1mm











8Daughter

Side view

1

2

3

4

5

6

7

1205742

1205741



120591 finally





120583rarr




120583rarr ]






119890of the ]











(a) (b)





Rang

e (m

m)

74

72

70

68

66

64

5060

70

X(m

m)

Y (mm)20304050607080





(a) (b)





References





















119888










120583V119890rarr













120583minus V119879










































































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




(a) (b)



5 CHORUS and DONUT


119890 ]120583and ]

120591) can


1 1198982and 119898



13= 1198982

3minus 11989821and








Interaction

Decay

120591

120591

120583












Beam

Anticounter

ShieldingFibre

trackers


Hexagonalmagnet


H ST

Spectrometer

120583

TV

sim15m















119888















am ax

is (120583

m)

800

700

600

500

400

300

200

100

0


Emulsionlayer

Emulsionlayer

Acetate base











120583rarr




120583rarr





Pb Emulsion layers


ECC brick

Electronicstrackers

120591

120591

1mm











8Daughter

Side view

1

2

3

4

5

6

7

1205742

1205741



120591 finally





120583rarr




120583rarr ]






119890of the ]











(a) (b)





Rang

e (m

m)

74

72

70

68

66

64

5060

70

X(m

m)

Y (mm)20304050607080





(a) (b)





References





















119888










120583V119890rarr













120583minus V119879










































































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




Beam

Anticounter

ShieldingFibre

trackers


Hexagonalmagnet


H ST

Spectrometer

120583

TV

sim15m















119888















am ax

is (120583

m)

800

700

600

500

400

300

200

100

0


Emulsionlayer

Emulsionlayer

Acetate base











120583rarr




120583rarr





Pb Emulsion layers


ECC brick

Electronicstrackers

120591

120591

1mm











8Daughter

Side view

1

2

3

4

5

6

7

1205742

1205741



120591 finally





120583rarr




120583rarr ]






119890of the ]











(a) (b)





Rang

e (m

m)

74

72

70

68

66

64

5060

70

X(m

m)

Y (mm)20304050607080





(a) (b)





References





















119888










120583V119890rarr













120583minus V119879










































































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics










119888















am ax

is (120583

m)

800

700

600

500

400

300

200

100

0


Emulsionlayer

Emulsionlayer

Acetate base











120583rarr




120583rarr





Pb Emulsion layers


ECC brick

Electronicstrackers

120591

120591

1mm











8Daughter

Side view

1

2

3

4

5

6

7

1205742

1205741



120591 finally





120583rarr




120583rarr ]






119890of the ]











(a) (b)





Rang

e (m

m)

74

72

70

68

66

64

5060

70

X(m

m)

Y (mm)20304050607080





(a) (b)





References





















119888










120583V119890rarr













120583minus V119879










































































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




am ax

is (120583

m)

800

700

600

500

400

300

200

100

0


Emulsionlayer

Emulsionlayer

Acetate base











120583rarr




120583rarr





Pb Emulsion layers


ECC brick

Electronicstrackers

120591

120591

1mm











8Daughter

Side view

1

2

3

4

5

6

7

1205742

1205741



120591 finally





120583rarr




120583rarr ]






119890of the ]











(a) (b)





Rang

e (m

m)

74

72

70

68

66

64

5060

70

X(m

m)

Y (mm)20304050607080





(a) (b)





References





















119888










120583V119890rarr













120583minus V119879










































































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




Pb Emulsion layers


ECC brick

Electronicstrackers

120591

120591

1mm











8Daughter

Side view

1

2

3

4

5

6

7

1205742

1205741



120591 finally





120583rarr




120583rarr ]






119890of the ]











(a) (b)





Rang

e (m

m)

74

72

70

68

66

64

5060

70

X(m

m)

Y (mm)20304050607080





(a) (b)





References





















119888










120583V119890rarr













120583minus V119879










































































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




8Daughter

Side view

1

2

3

4

5

6

7

1205742

1205741



120591 finally





120583rarr




120583rarr ]






119890of the ]











(a) (b)





Rang

e (m

m)

74

72

70

68

66

64

5060

70

X(m

m)

Y (mm)20304050607080





(a) (b)





References





















119888










120583V119890rarr













120583minus V119879










































































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




(a) (b)





Rang

e (m

m)

74

72

70

68

66

64

5060

70

X(m

m)

Y (mm)20304050607080





(a) (b)





References





















119888










120583V119890rarr













120583minus V119879










































































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




(a) (b)





References





















119888










120583V119890rarr













120583minus V119879










































































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics









119888










120583V119890rarr













120583minus V119879










































































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics





















































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics



review article the study of neutrino oscillations with emulsion...

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