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