search for rare signals and cr flux measurements: background rejection and montecarlo simulations

Search for rare signals and CR flux measurements:

background rejection and Montecarlo simulations

Roberta SparvoliRome “Tor Vergata” University and INFN

R. Sparvoli – MAPS 2009 -

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Outline of the lectures

Lecture 1:Lecture 1:

• Importance of rare signals in CR physics

• Detector strategies• “Existed” and “existing” detectors• Particle ID


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Outline of the lectures

Lecture 2:Lecture 2:

• Sources of background and their rejection

• Efficiencies & Contaminations• Absolute fluxes• Conclusions

Most of practical examples and results will be taken by the PAMELA experiment !


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Lecture 1:Lecture 1:Importance of rare signals

incosmic ray physics


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Everything starts with …


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Anti-nucleosyntesis

WIMP dark-matter

annihilation in the galactic

halo

Background:CR interaction with ISMCR + ISM p-bar + …

Evaporation of primordial black holes

and various ideas of theoretical interpretations


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Antimatter in early universe

The early Universe was a hot expanding plasma with equal number of baryons, antibaryons and photons. In thermal equilibrium the two-ways reaction was:

B + anti-B +

As the Universe expands, the density of particles and antiparticles falls, annihilation process ceases, effectively freezing the ratio:

- baryon/photon = antibaryon/photon ~ 10-18. - Annihilation catastrophe.

Instead, in the present real Universe: Baryon/photon ~ 6 * 10-10 (from direct observ. & microwave

background);Antibaryon/baryon < 10-4.


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Sakharov criteriaTo account for the predominance of matter over antimatter, Sakharov (1967) pointed out the necessary conditions occurring in the Early Universe:• B violating interactions;• non-equilibrium situation;• CP and C violation.

The processes really responsible are not presently understood!

GUT theories ? Leptogenesys ?


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Indirect ->By measuring the spectrum of the Cosmic Diffuse Gamma emissionBy searching for distortions of the Cosmic Microwave Background

Direct ->By searching for AntinucleiBy measuring anti-p and e+ energy spectra

What about the observations?

BALLOONS /PAMELA / AMS


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Direct searches: current status

PCR+HISM

PCR+HeISM p + anti-p secondary antiprotonsCR+HISM

CR+HeISM

• Antiprotons: DETECTED! secondary production

• Positrons: DETECTED! secondary production

• Anti-nuclei: never detected !They would be the real signature of antistars because their production by “spallation” is negligible

PCR+ ISMNCR+ISM + -> + -> e+

secondary positrons


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Antimatter Search: current limits


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Dark Matter searchesEvidence for the existence of an unseen, “dark”, component in the energy density of the Universe comes from several independent observations at different length scales:

Rotation curves of galaxies

Lensing

Large Scale StructureCMB

Galaxy clusters SN Ia

Bertone, Hooper & Silk, hep-ph/0404175, Bergstrom, hep-ph/0002126, Jungman et al, hep-ph/9506380


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The “Concordance Model” of cosmology

tot = 1.0030.010

m ~ 0.22 [b=0.04] ~ 0.74

Most of matter of non-baryonic natureand therefore “dark” !

The “concordance model” of big bang cosmology attempts to explain cosmic microwave background observations, as well as large scale structure observations and supernovae observations of the accelerating expansion of the universe.


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Different data:•WD supernovae•CMBR•Matter surveysall agreeat one point


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Energy budget of the universe

DarkEnergy:65%

DarkMatter:30%

22 %

74 %


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DM candidates: WIMP’s !SUSY particles ?


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SIGNALS from RELIC WIMPs

Direct searches: elastic scattering of a WIMP off detector nuclei

Measure of the recoil energy

Indirect detection: in cosmic radiation signals due to annihilation of accumulated in the centre of celestial bodies (Earth and Sun) neutrino flux

signals due to annihilation in the galactic halo neutrinos gamma-rays antiprotons, positrons, antideuterons


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Many things about CRs are known, but many others still remain uncertain.

A satisfactory model of propagation of CR in the Galaxy is not yet fully established. Different mechanisms play a role in the acceleration, propagation, diffusion, but the correct balance among them is still under debate.

Contemporary measurements of primary and secondary CR

elements


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A really CRITICAL point !

The effective possibility to disentangle exotic signal from pure secondary production depends strongly on the precise knowledge of the parameters which regulate the diffusion of cosmic rays in the Galaxy.Still uncertainties in the data (and in the cross sections !!) put limits on the interpretations.

For exotic physics searches


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Secondaries/primaries to constrain propagation parameters

D. Maurin, F. Donato R. Taillet and P.Salati ApJ, 555, 585, 2001 [astro-ph/0101231]

F. Donato et.al, ApJ, 563, 172, 2001 [astro-ph/0103150]

AstrophysicAstrophysicB/CB/C

constraintsconstraints

Nuclear Nuclear cross cross

sections!!sections!!

B/C Ratio Antiproton flux


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Lecture 1:Lecture 1:Detector strategies


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RedundanceTo search for rare particles in CR, an apparatus must have redundant information coming from its different subdetectors.

Only in this way it is possible to discriminate between the signal (very weak) and the background (very strong)

Rare particle detectors are composite


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Antimatter

Current values in CR:e+/(e+ + e-) ~ 10%antip/p ~ 10-4

Background limits:e+/p < 10-4 (> 10 GeV)antip/e < 10-2


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DefinitionsEfficiency = n. good events recognized good

n. good events

Contamination = n. bad events recognized good

n. bad events

Rejection factor = Efficiency

Contamination

High rejection factors needed !


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Detector strategy: sign of the charge

Main task: determine the sign of the charge deflection in a magnetic field

Charge of opposite sign would be deflected in opposite directions


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Magnetic spectrometersMagnetic field: it can be produced by a

permanent magnet or by a superconducting magnet.

For balloon missions: a superconducting magnet can be advantageous (intense field, no He evaporations problems)

For satellite/space stations missions: the problem of He evaporation can shorten the lifetime permanent more practical.


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Tracking system: it must lie inside the magnet, so to reconstruct – besides the charge - the curvature radius r.In a magnetic field:

r B = mv/Ze = p/Ze = R

Quantity measured in a spectrometer:

R (rigidity) = momentum/charge

Magnetic spectrometers


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Tracking systems

Must be very precise, since the curvature measurement error (R) depends on the spatial resolution and on the number of measurements along the track.

Maximum Detectable Rigidity (MDR):MDR = R/R = 1

Among the most used are Drift Chambers and Silicon detectors (strip pitch can be tuned to the desired resolution easily a few microns)

Momentum resolution and MDRex. PAMELA tracking system

MDR ~ 1 TV

mult. scatt. spat. resol. X

magnetic rigidity R = |pc/Z|

magnetic deflection η = 1/R = |Z/pc|

The higher the magnetic field strength, and the finer the granularity of the hodoscope’s tracking layers, the higher the rigidities that can be reached.


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Flight data: 0.169 GV electron

Flight data: 0.171 GV positron


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Detector strategy: time-of-flight

A system of scintillators used to determine the time needed by a particle to cross it.

Possibility to:• Trigger the acquisition;• Reject albedo;• Measure the particle ;• Measure the particle charge (dE/dx in scintillators)


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Detector strategy: time-of-flight

In addition, vs. R gives the particle mass, until a few GeV.


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Detector strategy: electron/hadron separation

An electromagnetic calorimeter, right after the spectrometer helps particles producing showers. In such a way, electron/hadron separation can be performed.

electron (17GV)hadron (19GV)


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Detector strategy: calorimeters

The choice of the “passive” materials composing the calo must be done thining that:

X0 (radiation length) ~ A/Z2

0(absorption length) ~ A 2/3

so one has to minimize X0 and maximaze 0 .

Generally: Lead/Tungsten interleaved with silicon strips/scintillating fibers


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Detector strategy: electron/hadron separation

To help discriminating electron from hadron, a neutron detector can be employed:

Different yield in neutrons between the showers.

ee++ ee++

pppp

Flight data PAMELA

Rigidity: 20-30 GV

Flight data PAMELA

Rigidity: 42-65 GV


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Detector strategy: particle velocity

(electron/hadron separation) To help futher rejecting the bkg, one can

add a detector measuring the velocity at high energy (above TOF).

Electromagnetic particles are relativistic, hadronic particles are slower:

Very useful to adopt a “threshold-effect” detector, emitting light/signal only at relativistic speeds.


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Detector strategy: particle velocity

Two types of detector:1) Cherenkov detectors: a particle

emits light only if > 1/n.

2) Transition Radiation Detectors: a highly relativist particles emits X-rays when crossing two different media.


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A single event in the RICH. The ring of Cherenkov light is clearly visible from a 1.3 GV electron at 8° incidence angle (CAPRICE94 data)


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Detector strategy: veto

Such a composite detector must be embedded in a veto system to minimize the background coming from outside.

The veto is generally made of scintillator in ON/OFF mode.

ATTENTION to veto in the main trigger !


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VETO in 2nd level Trigger

Anticoincidence -VETO used only in 2nd level Trigger high veto-rate by backscattering from CALO for good & rare events

GOOD EVENT BG Event – rejectedGOOD Event – VETO’ed

AC-VETO

CALO


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Lecture 1:Lecture 1:“Existed” and “existing”

detectors


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Stratospheric balloons


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The WiZard collaboration flights

CollaborationNew Mexico State University Tata Institute of Fundamental Research, Bombay Goddard Space Flight Center Royal Institute of Technology, Stockholm Centre de Recherches Nucleaires, Strasbourg Università di Perugia and INFN, Perugia INFN, Laboratori Nazionali di Frascati Università di Firenze and INFN, Firenze Università di Roma II and INFN, Roma Università di Trieste and INFN, Trieste Università di Bari and INFN, Bari

CAPRICE97

CAPRICE98


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OverviewAim of the activity is the detection of antimatter and dark matter signals in CR nei RC (antiprotons, positrons, antinuclei) for energies from hundreds of MeV to about 30 GeV, and measurements of primary CR from hundreds of MeV to about 300 GeV.

6 flights up to now: MASS89, MASS91, TRAMP-SI, CAPRICE 94, 97, 08. The flights started from New Mexico or Canada, with different geomagnetic cut-offs to optimize the investigation of different energy regions. The flights lasted about 20 hours. The instrument was built around a magnetic spectrometer (superconducting magnet, tracking system with multiwire or drift chambers). In additon, there was an imaging calorimeter below the magnet (streamer tubes in MASS 89 e 91, and tungsten/silicon in the following flights), a Time-Of-Flight system and, on top, a Gas-Cherenkov in the MASS flights, a TRD in TRAMP- SI and a Gas-RICH in the following flights.

TOF

TRACKING SYSTEM

TOFCALORIMETER

GAS CHERENKOV

1 m

MAGNET

MASS Matter Antimatter Space Spectrometer


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CAPRICE


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HEAT-pbar (High Energy Antimatter Telescope)

The HEAT-pbar CollaborationThe HEAT-pbar Collaboration

U of Chicago:U of Chicago: A. Labrador, D. MA. Labrador, D. Müüller, S.P. Swordyller, S.P. SwordyNorthern Kentucky U.:Northern Kentucky U.: S.L. NutterS.L. NutterIndiana U:Indiana U: A. Bhattacharyya, C. Bower, J.A. MusserA. Bhattacharyya, C. Bower, J.A. MusserU of Michigan:U of Michigan: S.P. McKee, M. Schubnell, G. Tarlé, A.D. S.P. McKee, M. Schubnell, G. Tarlé, A.D.

TomaschTomaschPenn State U.:Penn State U.: A.S. Beach, J.J. Beatty, S. Coutu, S. MinnickA.S. Beach, J.J. Beatty, S. Coutu, S. MinnickU. Minnesota:U. Minnesota: M. DuVernoisM. DuVernois

HEAT-pbar


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HEAT-pbar flights

Superconducting magnet spectrometer with Drift Tube Hodoscope (DTH)

Multiple Ionization (dE/dx) Detector

Time-of-Flight (TOF) system.


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HEAT-e flights

Superconducting Magnet Spectrometer with Drift Tube Hodoscope (DTH)

Electromagnetic Calorimeter (EC)

Transition Radiation Detector (TRD)

Time-of-Flight (TOF) system.

The BESS balloons The BESS balloons Balloon-borne Experiment with a Superconducting Spectrometer

Search for Primordial Antiparticles

antiproton: Novel primary origins (PBH,DM) (0.2 ~ 4 GeV)

antihelium: Asymmetry of matter/antimatter Precise Measurement of low energy Cosmic-ray flux: highly precise measurement at < 1 TeV

Proton (0.2~500 GeV) Helium (0.2~250 GeV/n)


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BESSCollaboration

The Universityof Tokyo

High Energy AcceleratorResearch Organization(KEK)

University of Maryland

Kobe University

Institute of Space andAstronautical Science/JAXA

National Aeronautical andSpace AdministrationGoddard Space Flight Center

University of Denver(Since June 2005)

BESS CollaborationBESS Collaborationas of April, 2006as of April, 2006


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The BESS program

The BESS program has had 9 successful flight campaigns since 1993.

A modification of the BESS instrument, BESS-Polar, is similar in design to previous BESS instruments, but is completely new with an ultra-thin magnet and configured to minimize the amount of material in the cosmic ray beam, so as to allow the lowest energy measurements of antiprotons.

BESS-Polar has the largest geometry factor of any balloon-borne magnet spectrometer currently flying (0.3 m2-sr).

BESS DetectorBESS DetectorRigidity measurement

SC Solenoid (L=1m, B=1T)– Min. material (4.7g/cm2)– Uniform field– Large acceptance

Central tracker Drift chambers (Jet/IDC) ~200 m

Z, m measurementR, --> m = ZeR 1/2-1dE/dx --> Z

JET/IDCRigidity

TOF, dE/dx

√

BESS-TeV Spectrometer

JET/IDC

MAGNET

TOF

ODC


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Satellite flights


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The PAMELA missionLaunched on the 15th July 2006 from Baikonur (Kazakhstan)..

In continuous data taking In continuous data taking since 11 July 2006 !!since 11 July 2006 !!


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The PAMELA collaboration

BariFlorenceFrascatiItaly:Italy:

TriesteNaples Rome CNR, Florence

Moscow St.

Petersburg

Russia:Russia:

Germany:Germany:Siegen

Sweden:Sweden:KTH, Stockholm


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Energy range Particles in 3 years

Antiprotons 80 MeV - 190 GeV O(104)

Positrons 50 MeV – 270 GeV O(105)

Electrons up to 400 GeV O(106)

Protons up to 700 GeV O(108)

Electrons+positrons up to 2 TeV (from calorimeter)

Light Nuclei up to 200 GeV/n He/Be/C: O(107/4/5) AntiNuclei search sensitivity of 3x10-8 in He/He

Design PerformanceDesign Performance

Simultaneous measurement of many cosmic-ray species

New energy range Unprecedented statistics


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Redundant instruments:

Spectrometer, made by a permanent magnet and a silicon tracking system (spatial resolution 4 m in bending view)

TOF (trigger, beta and charge)

Calorimeter EM (W-Si, 16.3 l.r., 0.7 l.i.;

rejection hadron/lepton > 104)

Neutron detector (by 3He counters) helps discriminating electromagnetic from hadronic cascades

~1.3m

G.F.: 21.5 cm2 sr Mass: 470 kgDim.: 130x70x70 cm3

Power: 360 W


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Space Station


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AALPHA MMAGNETIC SSPECTROMETER

Search for primordial anti-matter Indirect search of dark matter High precision measurement of the energetic spectra and composition of CR from GeV to TeV

AMS-01: 1998 (10 days)PRECURSOR FLIGHT ON THE SHUTTLE

AMS-02: 2010 COMPLETE CONFIGURATION FOR 3 YEARS LIFETIME ON THE ISS

» 500 physicists, 16 countries, 56 » 500 physicists, 16 countries, 56 InstitutesInstitutes


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AMS-02 : the collaboration AMS-02 : the collaboration

USAA&M FLORIDA UNIV.JOHNS HOPKINS UNIV.MIT - CAMBRIDGENASA GODDARD SPACE FLIGHT CENTERNASA JOHNSON SPACE CENTERUNIV. OF MARYLAND-DEPRT OF PHYSICSUNIV. OF MARYLAND-E.W.S. S.CENTERYALE UNIV. - NEW HAVEN

MEXICO

UNAM

DENMARKUNIV. OF AARHUS

FINLAND

HELSINKI UNIV.UNIV. OF TURKU

FRANCEGAM MONTPELLIERLAPP ANNECYLPSC GRENOBLE

GERMANYRWTH-IRWTH-IIIMAX-PLANK INST.UNIV. OF KARLSRUHE

ITALYASICARSO TRIESTEIROE FLORENCEINFN & UNIV. OF BOLOGNAINFN & UNIV. OF MILANOINFN & UNIV. OF PERUGIAINFN & UNIV. OF PISAINFN & UNIV. OF ROMAINFN & UNIV. OF SIENA

NETHERLANDSESA-ESTECNIKHEFNLR

ROMANIAISSUNIV. OF BUCHAREST

RUSSIAI.K.I.ITEPKURCHATOV INST.MOSCOW STATE UNIV.

SPAINCIEMAT - MADRIDI.A.C. CANARIAS.

SWITZERLANDETH-ZURICHUNIV. OF GENEVA

CHINA BISEE (Beijing)IEE (Beijing)IHEP (Beijing)SJTU (Shanghai)SEU (Nanjing)SYSU (Guangzhou)SDU (Jinan)

KOREA

EWHAKYUNGPOOK NAT.UNIV.

PORTUGAL

LAB. OF INSTRUM. LISBON

ACAD. SINICA (Taiwan)CSIST (Taiwan)NCU (Chung Li)NCKU (Tainan)

NCTU (Hsinchu)NSPO (Hsinchu)

TAIWAN


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AMS-01 : the detector AMS-01 : the detector

• Magnet: Nd2Fe14B, BL2= 0.15 TM2

• T.o.F: Four planes of scintillators;

• Tracker: Six planes of ds silicon detectors;

• Anticounters:

• Aerogel Threshold Čerenkov:

• Low Energy Particle Shielding (LEPS):

• Carbon fibre, shield from low energy (<5MeV) particles


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The AMS-02 detector• Superconducting Magnet (BL2= 0.85 Tm2)

• Silicon tracker (rigidity, charge)

• TOF Scintillators (β, dE/dx, trigger)

• Transition Radiation Detector (e/p)

• Ring Imaging Cherenkov (β, charge)

• Electromagnetic calorimeter (energy, e/p)

~2 m; 7 T

ons

~2 m

• Also gamma convert in ECAL

• Anticoincidence, star-tracker, GPS

• Acceptance: » 0.5 m2sr • Bending power » 0.8 Tm2

• TOF : trigger , , dE/dx (Z)• Tracker: § Q , R , dE/dx (Z<26) • RICH : , Z• ECAL : E, e/p • TRD: e/p


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Lecture 1:Lecture 1:Particle identification


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Particle identification

• Sign of charge and rigidity (tracker)• Absolute charge value (energy loss

in tracker/TOF scintillators)• Mass (TOF, RICH, TRD, …)• Electromagnetic/hadronic?

(calorimeter, ND)


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Identification of the charge sign and rigidity

The particle track is reconstructed by an algorithm fitting the impact points along the tracking planes;

The quality of the track is given by the of the fit; more the valid signals along the planes, better the fit;

The algorithm has a certain “efficiency”, since not always it converges in finding a track (too few signals or too many, when delta rays...).


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Spatial resolutionx = (2.77 ± 0.04) m

y = (13.1 ± 0.2) m

Beam-test data - orthogonally incident MIP

•Critically depends on the signal/noise ratio.

•Resolution for junction (X, bending) view determines the momentum measurement.


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A high-resolution spectrometer is needed to study rare particles.

Such a resolution in identifying the particle impact points in the system is useless if the mutual position of the tracker sensors are not known!

We need to express the impact point coordinates in a general reference frame (that of the whole apparatus)

Tracker alignment !

Identification of the charge sign and rigidity


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A priori alignmentOnce chosen a general reference frame, one can operate a simple a priori alignment knowing the position of the tracker sensors from the mechanical design of the detector. But ..• mechanical precision not enough! (f.i. 500 m vs 3 m in PAMELA)• possible variation of positions with time (stress, vibrations ..)


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Residuals

PAMELA 1° tracker plane: mechanical positions

PAMELA 1° tracker plane: after on-ground alignment

Distribution of the differences between the set of measured coordinates and those determined by the intersection of the fitted tracks


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A posteriori alignment

If the shape of the track is not known a priori, there are infinite combinations of different positions and curvatures which comply with the measured points. On the contrary, if the shape of the track is correctly reconstructed on the basis of its known deflection, and two positions in space are determined on the reference planes, the comparison between the other measured points and the expected ones results in a unique configuration of the sensor positions.


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Roto-traslational parameters

The alignment issue reduces to identify for each sensor the six parameters:

, , , x, y, z

Rotation matrix Traslation vector


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How to proceed?

At ground: a set of beam test data with known energy can do the job;

In flight: 1) switch off magnet and use

straight tracks (when possible)2) select with other detectors beams

of particles with known energy (electrons), or known direction (highly energetic protons)


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Alignment

Coherent misalignmentIt is equivalent to a systematic deflection error

Correction with electrons (or electrons + positrons)and comparison with simulation

Incoherent misalignmentThe systematic deflection error is null

Correction with protons

2 steps: column alignment + inter-column alignment

Alignment in PAMELA


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In-flight alignment (1/2)• Step 1: incoherent alignment.

• correction for random displacements of the sensors (~ 10 μm);

• done with relativistic protons;• minimization of spatial residuals as a

function of the roto-traslational parameters of each sensor. measured step 1

X side

Flight dataSimulation

After step 1:• spatial residuals are

centered;• measured width is

consistent with simulated combination of nominal resolution + alignment uncertainty (~ 1 μm).


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Comparison between simulation residuals (straight tracks) and flight dataresiduals from plane 2 and 3 of PAMELA tracker system.


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In-flight alignment (2/2)

After step 1, (possible) global distortions might mimic a residual deflection: ηmeas = ηreal+Δη.

0

Spe

P

Pz

*P0

PSpe

PCal~P0

t~0.1X0

e±

e±Step 2: coherent alignment.

• done with electrons and positrons;• cross-calibration CALO-TRK exploiting

brehmsstrahlung before spectrometer:

CALO energy uncertainty ±ε is symmetric for e- and e+ ;

spectrometer global distortion Δη gives a charge-sign dependent effect.

evaluated Δη ~ -10-3 GV-1

Δηηε1P

1

ηP

1~z

SpeCalSpeCal


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Identification of the absolute charge

Multiple dE/dx: p / - / e separationTechnique exploits the behaviour of the energy loss (Bethe-Bloch) in sensitive detectors:

2

2ln

2

11 22

max222

22

I

Tcm

A

ZKz

dx

dE e

Sentitive detectors: scintillators, silicon layers, …..


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Charge identification with TOF

dE/dx (MIP) in different planes as a function of beta

(saturation)


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e+

p

d

3He

4He

Li

Be

B,C

Charge identification with the Tracker

Average dE/dx (MIP) for 6 tracker planes as a function of Rigidity (GV)


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pp pp

dd

ee- - ee+ +

MASS from TOF: low energy


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MASS from RICH


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Electromagnetic/hadronic?

Of course, there is no problem in identifying an electron/positron against a non-interacting particle, due to the different patterns in the calorimeter;

The main difficulty is identifying an electromagnetic shower against a hadronic shower


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Flight data: 14.4 GVnon-interacting proton


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Flight data: 36 GV interacting proton


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Flight data: 1.56 GV positron


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Features to separate showers

1. Starting point of the shower;2. Fraction of detectable energy;3. Longitudinal profile;4. Transverse profile;5. Topological development.

Most of these features are energy dependent, so an efficient cut must take care of this.


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1. Starting point of the shower

E.m. showers are determined by the radiation length X0, hadronic by the absorption length 0.

With a suitable choice of the target material, these two quantities can differ of the order of 30 or so (ex. tungsten X0

= 0,35 cm and 0 = 10.3 cm)

This implies that an em shower starts much earlier in the calorimeter, generally within the first 2/3 planes !


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51 GV positron

80 GV proton

Shower starting-point


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2. Fraction of energy loss

A quasi-linear relation exists between the incident energy of an electron/positron and the energy released by the shower in the calo, until longitudinal leakage becomes important.

For hadronic showers, much energy is lost into excitation or break-up of the medium nuclei, or into neutrinos. Roughly 20% of the initial energy is non-visible.

The variable “energy-momentum match” well represents this difference in the two showers:


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ee--ee++

p, dp, dpp

‘Electron’

‘Hadron’

PAMELA flight data


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3. Longitudinal profileRegarding the longitudinal profile, the

parameter used to discriminating the two showers is the point of the shower maximum.

Due to the differences in X0 and 0, the e.m. shower maximum is easily contained until tens of GeV, and a logaritmic relation between the incoming energy and the position of the maximum can be established.

On the contrary, for hadronic showers the distribution of the shower maximum is rather randomly distributed.


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En

erg

y (m

ip)


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4. Lateral profileAn e.m. cascade, in its lateral profile, is characterized by the Moliere radius:

RM ~ ( 21 MeV X0 ) / Ec

where Ec is the critical energy (at which radiation losses equal collosion losses).Almost 99% of an e.m. shower is contained within 3.5 RM.

The spread of a hadronic shower is wider, due to the fact that the secondaries from the inelastic nuclear interaction are spread out with high transverse momentum.


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5. Topological development

For an e.m. shower, the multiplicity (total number of hit strips, and n. of hit strips/plane) is strongly correlated to the incident energy, while for hadronic shower – especially if not contained – this relation is much lose.

If, in addition, one focuses the multiplicity along the particle track, a simple discrimination between the two showers is possible.


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Fraction of charge released along the calorimeter track

LEFT HIT RIGHT

strips

plan

es

1 RM


PerugiaPAMELA flight data


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Neutron gain

search for rare signals and cr flux measurements: background rejection and montecarlo simulations

Documents

cosmic radiation signals

neutrino flux signals

supernovae observations

cc annihilation

independent observations

present real universe

annihilation catastrophe

b antib g gas