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Search for rare signals and CR flux measurements: background rejection and Montecarlo simulations. Roberta Sparvoli Rome “Tor Vergata” University and INFN. Outline of the lectures. Lecture 1: Importance of rare signals in CR physics Detector strategies “Existed” and “existing” detectors - PowerPoint PPT Presentation
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Search for rare signals and CR flux measurements:
background rejection and Montecarlo simulations
Roberta SparvoliRome “Tor Vergata” University and INFN
R. Sparvoli – MAPS 2009 -
Perugia
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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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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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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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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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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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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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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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
√
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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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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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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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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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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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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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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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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.
R. Sparvoli – MAPS 2009 -
Perugia
Fraction of charge released along the calorimeter track
LEFT HIT RIGHT
strips
plan
es
1 RM
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