the performance of the ams 02 silicon trackerricap09.roma2.infn.it/slides/haino_ams_ricap09r.pdf ·...
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The Performance ofthe AMS-02 Silicon Tracker
Evaluated during thepre-integration phase of the Spectrometer
S. Haino / INFN PerugiaAMS-02 Tracker Group
RICAP '0914/May/2009
Astrophysics with AMS-02
• Hadronic componentSec.-to-pri. ratios (e.g. B/C) : Propagation modelsConfinement time (e.g. 10Be/9Be) : Galactic halo modelsLong period observation : Solar modulation
• Indirect Dark Matter signatureAntiparticle spectrum (pbar, e+, Dbar)Gamma-ray flux
• Search for antinuclei• ... and something unexpected
Total electron flux – latest results
An example of DM interpretation
DM model :Bergström et al. [arXiv:0905.0333]
Nomura et al. [arXiv:0810.5397]
AMS-02
AMS-02 potential for e+ fraction
High energy limit mainly determined by
1. Spillover (e- contamination) Tracker is essential
2. Proton rejection
3. Statistics
AMS-02 Silicon Tracker• Tracker : 192 ladders in 8 layers• Ladder : 7~5 silicon sensors• Sensor : Double-sided, 640(p)+384(n) ch
LadderLadder
1 M
2 M3 M
4 M5 M6 M7 M9 M10 M11 M12 M13 M
2 P1 P
3 P4 P5 P
9 P7 P6 P
10 P11 P12 P
13 P
P - Side
Y
X
Layer 2
M - Side
640canali
Bending side (lato p)
Non bending side (lato n)
384canali
1.2m
N.Tomasse*
)110( mPY
µ=
)208( mPX
µ=
Topview
AMS-02 Tracker : requirements
• Position resolution for MIP vertical incidence~10 μm in p-side (Bending direction)
MDR > 2 TV (MDR > 4 TV for He)
• Alingment of 192 laddersA few μm accuracyMechanical stability
• Charge identification up to Fe (Z=26)
Alignment issues
• Mis-aligned tracker could give"excess" of antiparticles
• Momentum reference neededECAL(ΔE/E = 2~3% at 100 GeV)RICH(Δβ/β = 0.1% for Z = 1)No-B run (straight track : R = ∞)
AMS-02 Tracker Alignment plan
• Alignment on the ground (straight track)
• Launch (~150 dB vibration and ~3G acceleration)
• Alignment on the ISS (straight track)[Time limitation : a few days]
• Magnet excitation
• Alignment monitoring during the missionConsistency check with RICH, ECAL, TRDTAS (Tracker Alignment System)
Pre-integration at CERNSeptember/2007 ~ June/2008
• Cosmic-ray muon data taken for 6 monthsfor the performance check and debug
• "Nominal" runs with the stable DAQ andtracker thermal control for the last 2 months
•
No magneticfield
SiliconTrackerIntegra6onatCERN
11
Cosmic-ray data analysis
• Signal and noise check
• Alignment study
• Estimation of the position resolution
TIM, 21-25/ 07/2008
Alberto OlivaINFN / University of Perugia
Calibration Stability
• average dead channels fraction (DSP) = 0.04 (0.26) % for Y (X) side• average noisy channels fraction (DSP) = 2.11 (3.36) % for Y (X) side• average channel noise (<σ>) = 2.71 (3.31) for Y (X) side
318 calibrations (from 23 April to 10 Jun)
TIM, 21-25/ 07/2008
Alberto OlivaINFN / University of Perugia
Geometric Inefficiencies
1 mm
1 mm
• Out of ladders hits• Out of sensor hits
• Sensitive area is reduced to a fiducialarea due to “edges” effect (1 mm)
edges effect
Layer 2
TIM, 21-25/ 07/2008
Alberto OlivaINFN / University of Perugia
Signal Analysis (V): Ladders Gains• Inclination scaling, IA-IP and VA corrections• Refitting of the ladders Landau distributions• a Ladder gain global spread of 7 (4) % is been achieved
Ladders have a uniform behaviour (without corrections) at the 7%
TIM, 21-25/ 07/2008
Alberto OlivaINFN / University of Perugia
Signal Analysis (VI): Hit Correlation
• Applying all the correction a unique gain is been achieved
Cosmic-ray data analysis
• Signal and noise check
• Alignment study
• Estimation of the position resolution
Alignment parameters
• 5 of 6 parameters have been checkedfrom the mean of linear fitting residual andcorrected for each ladder (5×192 = 960 in total)- Translation (dx, dy, dz)- Rotation (dx/dy, dz/dx, dz/dy)
30~60cm3.
5cm
Alignment iterationBefore
After
Alignment accuracy estimationData divided into 5 samples (106 tracks each)
Alignment accuracy estimationData divided into 5 samples (106 tracks each)
Ladder alignment (Y) σ ~2.2 μm
Ladder alignment (X) σ ~2.0 μm
Statistical dependence: σ = p0+p1√N
Cosmic-ray data analysis
• Signal and noise check
• Alignment study
• Estimation of the position resolution
Multiple scattering and χ2 cutMC simulation
X Y: Bendingdirection
Residual distributions (two-gaussian fit)σ1:narrow gaussian, σ12:weighted mean
Test beam Results
Resolution estimationwith a simulation including multiple scattering
X
Y: Bending direction
Resolution VS angle (Ladder average)
Statistical dependece of resolutionStatistical dependence: σ = p0+p1√N
X
Y
Resolution VS SN ratioVertical incidence
X optimalY effective
X effective
Y optimal
MDR estimated with MC• dR/R2 is
porportinal to cos3θ cos2θ for 1/L2
cosθ for σ
Tracker
Tra
ck
Effective resolution
Intrinsicresolution
L2.8
1.3
CR data
MC
AMS-02
AMS-02 potential for e+ fraction
High energy limit mainly determined by
1. Spillover (e- contamination) Tracker is essential
2. Proton rejection
3. Statistics
AMS-02 spillover estimation
(1 TV)-1
p contamination (105 rejection)
Number of eventsA M S - 0 2 1 0 0 0 d a y s( e x p e c t e d )Fermi ~180 days (published)
PAMELA ~ 500 days (published)
e+ fraction – AMS-02 expected
DM parameters (2σ)
Bergström et al. [arXiv:0905.0333]Nomura et al. [arXiv:0810.5397]
DM model :
DM fit (2σ) – AMS-02 expected
Parametersassumed
Bergström et al. [arXiv:0905.0333]Nomura et al. [arXiv:0810.5397]
DM model :
AMS-02 expected(ATIC - KKDM model)
Conclusions
• Tracker performance estimated by CR muons
• Stable and uniform signal and noise level
• Alignment accuracy estimated as 2μm• Position resolution achieved as designed
(σy = 10 μm at θ ~ 0) agreed with Test Beam
• Spillover limit estimated from measuredresolution ~1 TeV for e+/e- separation