neutrino experiments - university of victoria · 2020-05-11 · neutrino experiments •20th...

Neutrino Experiments

Dean Karlen / University of Victoria & TRIUMF

Lake Louise Winter Institute, February 2010

Neutrino experiments

• 20th century – Foundation– Pauli-Fermi postulate

– discovery

– several basic properties determined

• Early 21st century – Detailed investigations– precision measurements with accelerators and reactors

• The Future– higher intensity beams

– larger scale detectors

• The story of solar neutrinos at SNO and the SNOLAB experiments will be covered by Aksel Hallin

LLWI 2010 2Neutrino Experiments / Karlen

Neutrino postulate

• In early 1900s, it was realized that some nuclei decay by emitting electrons, but the electron spectrum was not mono-energetic, as expected from energy conservation

• Bohr and others were willing to contemplate that energy conservation does not apply for such decays

• In 1930, Pauli proposed that some invisible particle shared the energy of the decay with the electron

• In 1933, Fermi proposed a theory to describe the process

LLWI 2010 Neutrino Experiments / Karlen 3

Search for the neutrino

• F. Reines and C. Cowan (both at Los Alamos) sought to detect neutrinos in the 1950s *– since neutrinos interact so weakly, an intense artificial

source would be needed

• Neutrino source:– initial idea: detonate a 20 k-ton fission bomb

– simultaneously drop a 1-ton underground detector about 50 m from the bomb (avoiding the shockwave?)

– proposal approved!

– during construction – idea was abandoned in favour of using a Nuclear Reactor as the source• the bomb idea has never been tried...


* an interesting account of their work: “Detecting the Neutrino”, R.G. Arns, Physics in Perspective, 3 (2001) 314

Reines and Cowan Reactor Experiments

• The first attempt used the Hanford Reactor in Washington State in 1953

• A large vessel containing 300 l of liquid scintillator was placed near the reactor


ne

90 two-inch photomultipliers

n

e+

neutron capture time reduced to < 10 mSby adding cadmium salts to the scintillator

Hanford experiment (1953)

• The 90 tubes were divided into two banks of 45 tubes

• when the two banks saw a coincidence (possibly from the positron annihilation) an “18 channel time-delay analyzer” with 0.5 ms channel width started

• a second coincidence within 9 ms would register a count in one of the 18 channels

• amplitudes of the pulses were also recorded in a 10-channel pulse height analyzer

• Detector was surrounded by lead and paraffin shielding to reduce the background from gammas and neutrons from the reactor



• Detected about 5 counts/min delayed coincidences, independent of the status of the reactor– they expected a neutrino rate of 0.1 – 0.3 counts/min for a

cross section of 6×10-20 barn (actually 12)

– the decay time distribution peaked at 3.5 ms and fell off exponentially “following closely the predicted function obtained in a Monte Carlo calculation for neutron capture in the detector.”

– the energy of the second pulse was characteristic of neutron capture

• Added a “GM blanket” in anticoincidence and a 2m thick water shield above the detector– no significant effect on rate



• The experiment had problems with the electronics, noise, and varying backgrounds from the reactor

– the dominant background were due to cosmic rays

• Results reported in Phys.Rev. Letter to the Editor:

– the popular media (NYT, Time, Scientific American, etc) all reported that the neutrino has been discovered



• The data that formed the basis for the first evidence of a neutrino were from relatively short runs taken at the end of the experiment (only a several hours of data taking)

– these runs had a higher than normal threshold for the first pulse: 2-5 MeV

– the effect was noticed after the end of the experiment at Hanford, so it could not be confirmed with a longer run


2.55 ± 0.15 counts/min

2.14 ± 0.13 counts/min

difference: 0.41 ± 0.20 counts/min

Hanford experiment (1953) - comments

• The techniques developed for the Hanford experiment form the basis for modern experiments studying detailed properties of neutrinos– A difficult experiment and a very good attempt

• After data taking completed, they noticed that data with a higher threshold for the positron:– reduced rate in background sample (5/min 2/min)– had a 2 sigma excess in counting rate for signal sample– of course, the efficiency for the signal would be lower as well in

this sample – but there is no comment– if the effect was real, it should have been observable in the

longer runs taken with lower threshold

• Appears to be a violation of a basic principle of data analysis: do not use the data itself to define its analysis– modern neutrino experiments employ blinding procedures to

avoid issues like this


Savannah River Experiment (1956)

• Reines and Cowan designed a new detector to measure inverse beta-decay

– two 200 l target tanks – filled with water and cadmium salt

– sandwiched by three scintillatortanks to detect the gammas

– looks remarkably like the most recently completed ndetector!



• Installed near Savannah River tritium production reactor

– 11 m of concrete shielding to reactor and 12 m of shielding from above to reduce cosmic background

• A similar delay circuit was setup to select events consistent with IBD:

– initial coincidence trigger for positron

– a second coincidence for neutron capture (3 < E < 11 MeV) delayed by several ms from the positron trigger

– delayed coincidences used to trigger oscilloscopes which were captured with film for analysis



• Example events:accepted: rejected:

• Many checks done to confirm events were from IBD:– dilute the target tank with heavy water (reduced rate)

– change concentration of cadmium salts (reduced capture time)

– increased the amount of shielding – reduced accidentals but did not affect the delayed coincidence rate


1

2

3

e+ n

tank


• A clear signal was present in early 1956– signal to background ratio: 3:1

– Reines and Cowan publish in Nature and Science that year• Running time: 1371 hr

• measured cross section “within 5% of 6.3 × 10-44 cm2”

• expected cross section 6.3 ± 1.5 × 10-44 cm2

• In 1957 – parity non-conservation in weak interactions discovered– expected IBD cross section: 10.0 ± 1.7 × 10-44 cm2

– In 1959 publish re-analysis of original data:• measured cross section: × 10-44 cm2

– In 1958 published results from a modified setup:• measured cross section: 11.0 ± 2.6 × 10-44 cm2


7

412

-

Savannah River Experiment (1956) - comments

• A much better experimental design with a clear signature– The change in the measured cross sections primarily

because efficiency not properly estimated for initial results

• Would the initial results have been released so quickly if they had not agreed well with the expected values?– lesson: avoid situation where decision to finalize analysis is

made on the basis of agreement with expectation• blinding procedures avoids this situation

• Note: 1953 signal rate: 25±12/hr cf. 1956: 2.9±0.2/hr– latter had larger targets and detector

• Despite importance of this work, and “changing numbers”, no attempt to confirm by a competing team


Discovery of a second neutrino (1962)

• Shortly after the neutrino was firmly established, a second type of neutrino was discovered at the BNL AGS:

– following independent proposals by Pontecorvo and Schwartz, a high energy neutrino beam was produced by directing high energy protons onto a target

• high energy neutrinos are produced by the subsequent decay of pions and kaons in flight

• downstream shielding absorbs all other beam particles



• Layout of the AGS experiment beamline:

– 15 GeV beam, 1.2 sec rep rate, 2-4 ×1011 protons in a 20-30 ms burst with 20 ns pulses separated by 220 ns

– beam timing is used to reduce cosmic background



• Layout of the AGS experiment detector:

– anticoincidencecounters to reducecosmic/punchthrough (B,C,D)

– trigger counters (A)

– each 1 ton block consists of 8 spark chamber gaps from1 in aluminum

– triggered eventswere photographed



• Example events:– selected events have

charged particlesoriginating downstream of the first few spark gaps

– 34 single particle events penetrate full detector, consistent with beingmuons

– only 5 shower events that could be electrons

– deduce that these eventsare produced by a secondkind of neutrino


Extra-terrestrial neutrinos

• The sun is a very intense source of neutrinos:

– flux on earth roughly 6 × 1010 /cm2/s

– observation would help understand solar model

• More challenging to observe:

– lower energy – most below 1 MeV

– continuous beam – more difficult to confirm backgrounds

• In 1964 a group, led by Raymond Davis Jr., proposed to detect solar neutrinos through the process:


Ar Cl 3737 -een

Homestake experiment

• The experiment used 615 tons of cleaning fluid, C2Cl4, in a deep mine – to reduce the effect of cosmic rays

– challenge: onlyabout 1 interactionexpected per day!

– every few months37Ar and otherimpurities were extracted though chemical purification

– 37Ar detected by its decay back to 37 Clt1/2 = 35 d


Homestake results

• A clear signal of 37Ar was seen – solar neutrinos detected

• Interestingly, only about 1/3 of the expected rate seen

• Aksel Hallin will talk about the resolution to that puzzleLLWI 2010 Neutrino Experiments / Karlen 22

An unexpected neutrino?

• In 1985, Simpson (Guelph) reported a difference from the expected electron spectrum from tritium decay


data could be explained bythe emission of a 17 keV n

in a few percent of the decays

b spectrum measuredwith a Si detector implanted with tritium

Research history on the 17 keV n

• Initially, other experiments did not support the claim

– but later, other groups saw effects consistent with a 17 keV neutrino in other nuclear decay spectra


DRO Morrison, Nature, 366 (1993) 29-32

null: solid stateand magneticspectrometers

Simpson: returns with new data and arguments against null expts

independent confirmation

Summary of results to 1991


Second generation expts (1992-1994)

• All null – convincing evidence against a 17 keV neutrino


Comments on the 17 keV neutrino

• How did seven experiments at 4 different institutions discover the same 17 keV neutrino that did not exist?

– the groups tried to understand the cause for the false positive signal:

• some found plausible explanations (backscattering, variation in source thickness, etc) others did not

– it is unlikely that different systematic effects could cause a distortion consistent with the same neutrino mass and mixing

• likely unconscious bias had something to do with this story

• In the end, the scientific method worked the way it should – it was interesting to see it in action


An unexpected neutrino burst

• On February 23, 1987 a nearby supernova was observed

– close enough to be seen by eye

• Neutrinos take away 10000 times more energy than photons – some 1057 were emitted in a few seconds

– could they be detected?


before after


• Two large detectors, originally designed to detect the decay of a proton a large volume of water,

– IMB (Irvine-Michigan-Brookhaven) in Ohio

– Kamiokande (Kamioka Nucleon Decay Experiment)

were operating at the time. They looked through their data for a burst of high energy neutrinos near the time of the observation of the supernova...

• Luckily, both of these detectors had upgraded their sensitivity with improved phototubes not long before the supernova!


Large water detectors

• Relativistic charged particles passing throughwater emit Cherenkov light in a forward cone

– provided velocity > c/n (n=1.33 for water)

– cone angle in water is 42 for b=1

• Like the 1953 Reines/Cowan experiment,phototubes surround the volume

• The water acts both as the neutrino target and the Cherenkov radiator


IMB

Kamiokande - II


• Kamiokande-II:

– 2140 ton water

• IMB:

– 6800 ton water

• Baksan (Russia):

– 200 ton scintillator

• Absolute timing of the dataevents were known to only~1 min for Kamiokande andBaksan


Neutrino astronomy

• SN 1987A was the first distant source of neutrinos observed – opened a new type of astronomy

– SN models predict that the neutrino burst can arrive hours before the first light – thus providing an early signal for astronomers


SN 1994D in NGC 4526

hubblesite.org

SuperNova Early Warning System

Number of neutrino types

• Starting in 1989, the Standard Model of particle physics was about to be put to the test at 2 new accelerators designed to produce large numbers of Z0 bosons

– SLC at SLAC and LEP at CERN: ee- Z0

• The known quarks and leptons were arranged in three generations, each with one neutrino (e, mu, tau)

– the top quark and tau neutrino had not yet been observed

• The Standard Model predicts Z0 decay rates to fermions

– additional neutrino types would imply a shorter Z0 lifetime or equivalently broader Z0 lineshape than expected


LEP at CERN

• Before the LHC, the tunnelwas used for the LEP ee-

accelerator

– four general purposedetectors


OPAL

Number of neutrino types

• Rapid progress... for example:

– 08/14/89 SLC: Nn = 3.8 ± 1.4

– 01/10/90 OPAL: Nn = 2.73 ± 0.26

• Summary from all LEP experiments: Nn = 2.984 ± 0.008


SLC - 1989

LEP

Another way to count neutrinos at LEP

• A direct measurement of neutrino production was also performed:

– ee- nn could not be measured, because the neutrinos escape detection

– instead, measure ee- nng in which the photon is seen and the imbalance of transverse momentum indicates that invisible particles were produced: hermetic detector

• First result (OPAL 1990)

• All LEP data:Nn = 2.92 ± 0.05


Finding the third neutrino

• To confirm that a third type of neutrino exists (one that produces tau leptons) a special purpose beamline and experiment was designed at Fermilab

• Challenge #1:

– need a large flux of nt

• 20kW of 800 GeV protons strike target

• Ds decays to t + nt and t decays to nt



• Challenge #2: distinguishing a t from other particles produced by electron and muon neutrinos

– use short decay length

• emulsion plates andscintillating fibresembedded intoiron target

• require evidence for short lived particle

• required that no e orm produced atevent vertex



• The final analysis selected 9 events consistent with nt

– an expected background of 1.5 events• charm production by ne or nm

• secondary interaction, mimicking a short lived particle

• Their first paper (discovery) states:– “The Poisson probability of the background fluctuating to the

signal level is 4.0 × 10-4”

and in its conclusion it states:– “The probability that the four events are from background

sources is 4 × 10-4, and we conclude that these events are evidence that t neutrino charged current interactions have been observed”

• Do you see a problem with the conclusion?


Mixing Neutrinos

• If neutrinos have different masses, the mass eigenstatesdo not have to be the flavour eigenstates

– the flavour eigenstates ne , nm , nt can be mixtures of the mass eigenstates n1, n2, n3

– The mixtures can be described by a matrix, U

• An experiment can produce a neutrino of a definitive flavour (by identifying the charged lepton in the reaction)

– The flavour of the neutrino can be different when it is detected at a later time because of the different frequencies in the propagation amplitudes...


i

i

iU nn 3

1

*

Neutrino oscillation

• The propagation of the mass eigenstates are:

– in the relativistic limit this is equivalent to:

– and the probability for the neutrino to oscillate into another flavour is:


)0()( i

tim

iiet nn -

)0()(2/2

i

ELim

iieL nn -

-

ji

ijij

ji

ijij

ELmW

ELmWLP

2

222

2/sin Im 2

4/sin Re 4)()( bbb nnnn

**

jjiiij UUUUW bb

E

Lm

E

Lm ijij GeV

kmeV27.1

4 2

22

Neutrino mixing matrix

• The mixing matrix, U, is usually decomposed as:

– where cij = cos qij and sij = sin qij

– if the phase is non-zero, neutrino and anti-neutrino oscillation probabilities differ: CP violation

– the phases, x1 and x2, are zero unless


-

-

-

-

-

100

00

00

100

0

0

0

010

0

0

0

001

2/

2/

1212

1212

1313

1313

2323

2323

2

1

x

x

i

i

i

i

e

e

cs

sc

ces

esc

cs

scU

ii nn

Evidence for neutrino oscillation?

• In 1995, the Liquid Scintillator Neutrino Detector experiment at Los Alamos reported seeing oscillations

– L = 30 m

– E ~ 50 MeV

– m2 ~ eV2

• Used a scaled upversion of the originalReines/Cowan exptto detect inversebeta decay


enn m

First results from LSND

• Conflicting analyses published back to back:

– observes 9 events with expected background of 2.1±0.3

– observes 5 events with expected background of 6.2


Definitive evidence for neutrino oscillation

• Neutrinos produced by cosmic ray interactions in the atmosphere were studied for many years by the large proton decay experiments

– anomalies noted by some

• In 1998, the Super-Kamiokande experiment presented striking evidence for neutrino oscillation

– left no doubt that neutrinos do oscillate and therefore are not massless, as many had thought


Super Kamiokande

• In 1996 the SK detectorcame online

– 50 kt water, 22 kt fv

– 30 times morefiducial mass thanKamiokande

– 11k 20-in phototubes

– 1 km underground


Kamiokande

Super Kamiokande

• Replacement of most of thephototubes took place in2005-2006


Atmospheric neutrinos

• High energy hadronic interactionsproduce muon and electronneutrinos in roughly 2:1 ratiofor En < 5 GeV– ratio increases above that

• In absence of oscillations, the fluxis up-down symmetric– downward neutrinos have

travelled some 15 km

– upward neutrinos have travelledsome 13,000 km

– up-down measurement is sensitive to oscillation lengths in 100-10,000 km range


Distinguishing electron and muon neutrinos

• Electrons produced from CC interactions generate showers – fuzzy Cherenkov rings

• Muons produce much sharper rings


Electron-like Muon-like

Results

• First presentedat “Neutrino ‘98”

– electron neutrinoflux in agreementwith no-oscillationmodel

– significant deficitof upward goingmuon neutrinos



SK-I dataMonte Carlo (no oscillations)Monte Carlo (best fit oscillations)

Now with much more data. Best fit: m2 ≈ 2.5 × 10-3 eV2 and sin22q ≈ 1

Neutrino experiments in the 21st century

• Atmospheric neutrinos revealed an oscillation with:

m2 ≈ 2.5 × 10-3 eV2

• Solar neutrinos revealed a much smaller m2 :

m2 ≈ 8 × 10-5 eV2

– n1 and n2 have nearly the same mass

• To improve our understanding of the phenomena, return to the discovery facilities: reactors and accelerators


facility En L (m2=8 × 10-5 eV2)solar

L (m2=3 × 10-3 eV2)atmospheric

Reactor 4 MeV 100 km 2 km

Accelerator 1 GeV 20,000 km 500 km

Reactor experiments

• Mean energy observed is approximately 4 MeV

– Only disappearance measurements are possible

– Cannot explore the imaginary component of U


-

ji

ijij

ji

ijij

ELmW

ELmW

LP

2

22

2

2/sin Im 2

4/sin Re 4

)()(

b

bb

nnnn

**

jjiiij UUUUW bb

en

Kamland

• 1000 tons of LS in a balloonimmersed in mineral oil andsurrounded by 1879 PMTsmounted on a sphere sittingin water

– outer PMTs veto muons


Kamland

• Detects neutrinos frommany reactors at differentdistances

– 80% of neutrinos comefrom L = 130-220 km


Kamland observed spectrum

• Reactor records and model defines expected spectrum


Kamland results


∆m2 = 7.58 ×10-5 eV2

tan2θ12 = 0.56

+0.21-0.20

+0.14-0.09

12

Reactor experiments – short baseline

• IBD experiments placed 1km from the reactor are sensitive to the 1-3 elements of the mixing matrix:

• So far, short baseline experiments have not detected a spectral distortion

– The best limit comes from the Chooz experiment


ELmP ee 4/sin2sin1)( 2

13

2

13

2 - qnn

232

13

13

2

eV 105.2for

C.L. 90% @ 15.02sin

-

m

q

Chooz

• Located in Northern France

– 5 ton LS with Gd

– collected datain 1997-98

– 3600 eventscollected

– bkgnd = 10%


Chooz results

• To improve sensitivity – new experiments planned:

– more events

– include an identical near detector reduce sensitivity to modelling the reactor and the detector acceptance


Double Chooz

• Building an improved detector

– larger target: 8.8 ton

– four concentric volumes

• target: LS with Gd in acrylic

• g-catcher: LS in acrylic

– avoids boundary effects

• 390 phototubes in mineraloil buffer

• outer cosmic muon veto

• Phase 1 to start in 2010

• Phase 2 – duplicate detector400 m from reactors


Double Chooz construction

• From summer and fall 2009...


Double Chooz goals


CHOOZ Double Chooz

Target

volume5.55 m3 10.3 m3

Data taking

periodfew months 3-5 years

Event rate 2700Far: 4 104/3y

Near: 5 105/3y

Statistical

uncertainty2.7% 0.5%

Reactor 2.1% <0.17%

Detector 1.64% <0.28%

Scintillator

lifetimefew % 0.25%

Analysis 1.5% 0.3%

Systematic

uncertainty2.7% <0.6%

Sensitivity to sin22q13

Reno

• A similar experiment underconstruction in Korea

– target mass 16.6 ton

– double reactor power

– sensitivity goal: sin22q13 =0.02

– start operation later this year


100m 300m

70m high

200m high

1,380m290m Far Detector

Near Detector

Reactors

http://reno01.snu.ac.kr/~reno/wiki/index.php/Image:Tdr_3-2.jpg

http://reno01.snu.ac.kr/~reno/wiki/index.php/Image:Tdr_3-2.jpg

Daya Bay

• Sited near Hong Kong – China+Russia+Czech+US collab.

• Multiple identical detectors at three sites

– 4 detectors at far site, 2 detectors at the 2 near locations

– compare detectors at same site to confirm systematic errors

– tunnels between detectorlocations allow them tobe exchanged if the systematic errors dictate

– DB near detector may start datataking this year, all sites in 2011


Daya Bay detectors

• Standard “3-zone”design – target, g-catcher,and MO buffer


Gd-Loaded LS

(20 tons)

LS

Mineral Oil

5 m

Water Pool

RPCs

Comparison of SBL reactor experiments

• Coming on line later this year or next year:

• The experimental design concepts are very similar

– ideally would like to see confirmation by alternative techniques (which is the case for the accelerator expts)

– could all three make the same mistake?


Experiment Power (GW)

L near/far(m)

Depth n/f (mwe)

Target mass (tons)

sin22q13

sensitivity*

Double Chooz 8.6 410/1050 115/300 8.8/8.8 0.03

RENO 17.3 290/1380 120/450 16/16 0.02

Daya Bay 17.4 363-1985 260/910 40,40/80 0.01

* 90% CL rough estimate – after 3 years running

21st century accelerator experiments

• Several accelerator neutrino experiments undertaken to probe neutrino oscillations

– protons on target to produce muon neutrinos

– appearance and disappearance measurements


Project Accel P (MW)

<En> (GeV)

L(km)

m2* (eV)2

goal

K2K KEK 0.005 1.4 250 0.007 atmospheric, q13

MiniBooNE FNAL 0.05 1 0.5 2.5 LSND

MINOS FNAL 0.25 2-6 735 0.003- 0.01

atmospheric, q13

CNGS CERN 0.12 20 730 0.03 tau appearance

T2K J-PARC 0.7 0.7 295 0.003 atmospheric, q13

Nova FNAL 1 2 810 0.003 atmospheric, q13

* the value for which the oscillation is maximized

Matter effect in neutrino oscillation

• For high energy neutrinos passing through matter, it is important to account for the fact that electron neutrinos have CC coupling to electrons, whereas the other flavours do not

– this modifies the appearance probability,by including multiplicative factors ,where:

– the sign depends on whether it is n or n and on the sign of

– use this to determine hierarchy


)( eP nn m

)1( nx-

GeV 12

222

31

nnn

E

m

ENGx eF

n3

n2n1

n2n1

n3

2

31m

normal inverted

Producing the neutrino beam

• The beam requirements for neutrino oscillation experiments can only be met by including focussing elements after the target:

– long baseline requires high intensity

– oscillation studies best done with pure neutrino (anti-neutrino) beam

• All neutrino beam facilities include magnetic horns:


B

pp

p

p-

Producing the neutrino beam

• After focusing with one or more horns, the charged hadrons are allowed to decay in flight in a decay pipe

– To produce a nm beam, focus p

– Allow enough distance for

– Not too long or else too many

• Depending on the physics goal, beams typically have ne

contamination at the 0.1 – 1% level

• At the end of the decay pipe, special beam dumps are in place to absorb all remaining particles and dissipate the heat.


mnmp

mnnm e

e

Off-axis concept

• With the majority of the nm coming from two body decay, the neutrino spectrum has a strong angular dependence

– off-axis spectrum is narrower – good for oscillation studies


NOvA

Accelerator neutrino oscillation experiments

• For the very long baselines 200-800 km, the far detector must be massive, otherwise the event rate will be too small

• Large volume detectors find another role

– Water Cerenkov detectors (eg. Super Kamiokande)

– Coarsely segmented scintillator or steel scintillator

• To study both disappearance and appearance, lepton flavour identification is essential

– and distinguish electrons from p0s produced in neutral current interactions which mimic an ne CC interaction



• Unlike for reactor experiments:

– neutrino flux and spectrum are not well understood

– neutrino interaction cross sections and kinematics are not well measured

– the spectrum of neutrinos varies with location

• For this reason auxiliary datais required:

– near detector(s) for event rates and kinematic studies

– dedicated hadron production experiments



• Near detectors

– measure the profile of the beam

– measure the spectrum and rate, F(En) × s(En), prior to neutrino oscillations for both nm and ne

– measure the kinematics of neutrino interactions – to better understand possible backgrounds at the far detector

– to do all this, it may be a good idea to have more capable near detectors than the far detector – but target material should be the same as the far detector, if possible

• Hadron production experiments

– measure the production rate of p and K for a beam and target of similar properties – to better estimate the n flux


K2K

• The first long baseline neutrino oscillation experiment

• Used the existing 12 GeV KEK-PS to direct an on-axis beam towards SK between 1999 and 2004

– experiment ended when a horn inner conductor broke

• In total 1020 protons delivered on target


K2K

• For the K2K neutrino spectrum a large fraction of the interactions are charged current quasi-elastic (CCQE):

– The neutrino energy can be calculated from the muonalone:

– the proton is typically below Cerenkov threshold

– neglects Fermi motion, which smears resolution by ~10%

– CC non-QE interactions will reconstruct a lower neutrino energy


pn mn m

mmm

mm

nqcos

2/2

pEm

mEmE

N

Nrec

-

-

K2K result

• The statistics were limited, but the results consistent with the atmospheric neutrino oscillation measurements


112 events observed158±9 expected no osc58 single-ring m like

MINOS

• Main goal: measurenm disappearance

• Far detector:

– 5.4 kT, 8×8×30 m3

– steel/scintillator

• Near detector:

– 1 kT, 4×5×15 m3


92.9 % nm

5.8 % nm

1.3 % ne + ne

MINOS events

• Typical events

– CC events to study disappearance to nt and ne

– NC events used to study disappearance to a sterile neutrino – no evidence for this


MINOS – nm disappearance

• Total POT analyzed: 3 × 1020 (Data from 2005-2007)

• Observed 848 events (expect 1060±60 if no oscillations)


Reconstructed neutrino energy (GeV)

Even

ts G

eV

MINOS – ne appearance

• Discrimination is difficult: look for compact showers

– ANN algorithmdeveloped with11 observables

– S/B 1:4

– backgroundconfirmed byHorn-On/Offstudies


M. SanchezISU/ANL


• Total POT analyzed: 3 × 1020

• Background prediction is 27 ± 5(stat) ± 2(sys)

• At the Chooz limit, would expect 6-12 signal events

• Analysis done ina blind fashion

• Observe 35 events



• Starting to be competitive with the Chooz result

• expect new result with 7 × 1020 POTsoon


OPERA

• An ambitious experiment to observe nt appearance

– High energy neutrino beam: to allow nt CC production of t

– Scale up the DONUT concept to 1.25 kT of emulsion target

• Beam:

– <En> = 17 GeV

– ne contamination = 0.9 %

– nt contamination isnegligible

• Expectations in 5 years:

– 10 t events, <1 background


CERN

LNGS

OPERA

• 150,000 bricks produced, each with 57 emulsion layers


10.2 cm

12.5 cm7.5 cm

10 X0

OPERA Film2 emulsion layers (44 mm thick)

poured on a 205 mm plastic base

1mm

0.3mm

Lead plate

OPERA detector


SM1 SM2

Target area (ECC + CS + TT)

Muon spectrometer (Magnet+RPC+PT)

Brick Manipulator System A. Ariga WIN’09

OPERA

• Candidate events are selected using the surrounding tracking detectors – bricks with vertexes are scanned by one of 10 labs around the world

• 2008 run: 1.7 × 1019 POT delivered

– 1600 neutrino interactions on emulsion targets

– expected t signal: 0.7 events, no t candidates

– 15 charm candidates:

• 2009 run: 3.5 × 1019

POT delivered


muon

Lead plate (1 mm)

vertex

D0

A. Ariga WIN’09

MiniBooNE

• The excess of reported by LSND would correspond to a third mass splitting, m2 ~ eV2

• The MiniBooNE experiment was designed to test the neutrino oscillation interpretation, using a similar L/En, but about 17 times larger L and En.

– different signature and systematics


enn m

W.C.Louis

Detector:• 12 m diameter• 800t of mineral

oil (CH2)• 1280 inner PMTs

MiniBooNE – ne appearance

• Initial result (2007) was based on 5.6×1020 POT

• The experiment performed a blind analysis:– After the analysis cuts were set, an oscillation fit was

performed in the energy range 300 < En < 3000 MeV

– Only the goodness of fit was returned - and was found to be poor for only one observable, Evis: p-value = 0.01

– There was suspicion about the modelling of low energy backgrounds. By raising the minimum En to 475 MeV, the number of background events expected would be significantly reduced and have little effect on the sensitivity to oscillation parameters

– It was therefore decided to perform the fit over the range 475 < En < 3000 MeV and open the box...


MiniBooNE – ne appearance

• In the defined signalregion there was nosignificant excess

• Below 475 MeV theexcess was 96 ± 17 ± 20,possibly from anotherbackground source

• LSND oscillation hypothesis ruled out with p-value = 0.02


MiniBooNE – ne and ne appearance

• Improved analysis of low energy region, modeling of backgrounds, and 15% increased statistics

– excess reduced but still present 3.5 s 3.0 s

• Data was collected with the horn polarity reversed in order to search for

oscillations

– no excess seen for either En > 475 MeV or En < 475 MeV

• Stay tuned for moredata from MiniBooNE


enn m

T2K and NOvA

• Next generation long baseline neutrino experiments– high beam power ~1 MW

– off-axis approach – L/E chosen for m2 = 0.003 eV2

• Different approaches:– T2K (Japan)

• uses Super Kamiokande as far detector (water Cerenkov)

• sophisticated near detector complex

• <En> = 0.7 GeV: mass effect is small and CCQE is large fraction of interactions

– NOvA (US)• building new near and far detectors: liquid scintillator in

extruded channels – same technology for both

• <En> = 2 GeV: mass effect is larger, CCQE is small fraction of interactions


T2K – 295 km across Japan


February, 2004

T2K - status

• Neutrino beam commissioning started April 2009


T2K - status

• Near detectors:

– On axis:14 ten-tonmodules

– Off axis:water,scintillator, andtime projectionchambersall in a dipolemagnet (ex-UA1, Nomad)


T2K - first neutrino event


MR Run #27Shot #19655T2K Spill #241792

Iron (6.5cm thick)

Plastic scintillator(5cm wide, 1cm thick)

Hit in plastic scintillator

INGRID Mod 07

T2K - first off axis neutrino event


Pi-zero detector (P0D) Tracker ECAL

TPC1 TPC2 TPC3FGD1 FGD2

n beam direction

(not yet operating)

(not fully read out)

T2K – off axis with magnet powered


• The near detector tracker design – remarkably similar in concept to the Savannah River experiment!

T2K – sensitivity

• Atmospheric oscillation:

• Sensitive to or less (depending on )


01.02sin ,10 23

242

23 - q m

01.02sin 13

2 q

NOvA

• Far detector 14 mrad off axis the existing NuMI beamline


NOvA detectors

• Near and far based on same concept – LS + WLSF + APD


15 kton357,000 cells

NOvA far detector hall

• Prior to winter... scheduled to start mid-2013


Reactors and Accelerators

• A view into the crystal ball from NOvA:


M. SanchezISU/ANL

CP violation

• Combining T2K and NOvA – 1 and 2 s contours:


G. FeldmanHarvard

Resolving the mass hierarchy

• It depends on q13 and


G. FeldmanHarvard

Beyond T2K and NOvA

• If q13 is small, measuring CP violation in neutrino oscillations becomes very difficult

– requires more intense beams, larger far detectors

– a broader range of science may be needed to justify costs

• Some ideas:

– superbeams: proton driver – go beyond 1 MW

• eg possible future JPARC upgrade, FNAL project X

– beta beams: storage ring with radioactive isotopes – those decaying along a straight section provide a ne beam

– as a first step toward a muon collider, build a muon storage ring – muon decaying along a straight section form an energetic neutrino beam (mix of nm and ne)


FNAL LBNE

• In January the Long Baseline Neutrino Experiment completed CD-0 phase (mission need)

– plan to direct a superbeam 1300 km to the DUSEL site

• possibly 300 kton of water Cerenkov

• possibly a large LAr detector


Large LAr TPCs

• ICARUS:

– 600 ton LAr TPC at LNGS to start data taking in April

• MicroBooNE:

– 100 ton LAr TPC at FNAL booster

• concepts for many kton LAr TPCs for the future...


Conclusions

• Doing experiments with neutrinos is very challenging given how difficult it is to detect them– Part of the allure – perhaps they hide something profound

about the Universe

– When doing difficult experiments, we can sometimes fool ourselves – but the scientific method eventually sets us straight

• Neutrino science has grown tremendously in the past two decades – and several new projects are about to get underway– could not cover all – notably 0n2b and direct mass

– stay tuned for more interesting results in the coming years


neutrino experiments - university of victoria · 2020-05-11 · neutrino experiments •20th...

Documents