The Performance of the AMS - 02 Silicon Tracker Evaluated during the - - PowerPoint PPT Presentation

The Performance of the AMS-02 Silicon Tracker

Evaluated during the pre-integration phase of the Spectrometer

• S. Haino / INFN Perugia

AMS-02 Tracker Group

RICAP '09 14/May/2009

Astrophysics with AMS-02

• Hadronic component

Sec.-to-pri. ratios (e.g. B/C) : Propagation models Confinement time (e.g. 10Be/9Be) : Galactic halo models Long period observation : Solar modulation

• Indirect Dark Matter signature

Antiparticle 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

Ladder Ladder

1 M 2 M 3 M 4 M 5 M 6 M 7 M 9 M 10 M 11 M 12 M 13 M 2 P 1 P 3 P 4 P 5 P 9 P 7 P 6 P 10 P 11 P 12 P 13 P

P - Side

Y X

Layer 2

M - Side

640 canali Bending side (lato p)

Non bending side (lato n) 384 canali

1.2
m

N.
Tomasse* ) 110 ( m P

Y

µ =

) 208 ( m P

X

µ =

Top
view

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 ladders

A few μm accuracy Mechanical stability

• Charge identification up to Fe (Z=26)

Alignment issues

• Mis-aligned tracker could give

"excess" of antiparticles

• Momentum reference needed

ECAL(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 mission

Consistency check with RICH, ECAL, TRD TAS (Tracker Alignment System)

Pre-integration at CERN

September/2007 ~ June/2008

• Cosmic-ray muon data taken for 6 months

for the performance check and debug

• "Nominal" runs with the stable DAQ and

tracker thermal control for the last 2 months

• No magnetic

field

Silicon
Tracker
Integra6on
at
CERN

11

Cosmic-ray data analysis

• Signal and noise check
• Alignment study
• Estimation of the position resolution

TIM, 21-25/ 07/2008 Alberto Oliva INFN / 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 Oliva INFN / University of Perugia

Geometric Inefficiencies

1 mm 1 mm

• Out of ladders hits
• Out of sensor hits
• Sensitive area is reduced to a fiducial

area due to “edges” effect (1 mm)

edges effect Layer 2

TIM, 21-25/ 07/2008 Alberto Oliva INFN / 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 Oliva INFN / 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 checked

from the mean of linear fitting residual and corrected for each ladder (5×192 = 960 in total) － Translation (dx, dy, dz) － Rotation (dx/dy, dz/dx, dz/dy)

30~60cm 3.5cm

Alignment iteration

Before After

Alignment accuracy estimation

Data divided into 5 samples (106 tracks each)

Alignment accuracy estimation

Data 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 cut

MC simulation

X Y: Bending direction

Residual distributions (two-gaussian fit)

σ1:narrow gaussian, σ12:weighted mean

Test beam Results

Resolution estimation

with a simulation including multiple scattering

X Y: Bending direction

Resolution VS angle (Ladder average)

Statistical dependece of resolution

Statistical dependence: σ = p0+p1√N

X

Y

Resolution VS SN ratio

Vertical incidence

X optimal Y effective X effective Y optimal

MDR estimated with MC

• dR/R2 is

porportinal to cos3θ

cos2θ

for 1/L2

cosθ for σ

Tracker Track Effective resolution Intrinsic resolution L 2.8 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 events

A 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

Parameters assumed

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 measured

resolution ~1 TeV for e+/e- separation