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. 10 Be/ 9 Be) : 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 potential for e + fraction AMS-02 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 Bending side (lato p) ( P 110 m ) = µ Y 640 canali Ladder Ladder 1.2
m Non bending side (lato n) ( P 208 m ) = µ X Y Layer 2 384 1 M canali Top
view 2 M 3 M 13 P 4 M 12 P 5 M 11 P 6 M 10 P 7 M 9 P 9 M 7 P X 10 M 6 P 11 M 5 P 12 M 4 P 13 M 3 P 2 P 1 P M - Side P - Side N.
Tomasse*

AMS-02 Tracker : requirements • Position resolution for MIP vertical incidence ~ 10 μ m in p-side (Bending direction)  MDR > 2 TV (MDR > 4 TV for He) • Alingment of 192 ladders A few μ m accuracy Mechanical stability • Charge identification up to Fe ( Z =26)

Alignment issues • Mis-aligned tracker could give "excess" of antiparticles • Momentum reference needed ECAL( Δ E / E = 2~3% at 100 GeV ) RICH( Δ β / 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

Calibration Stability 318 calibrations (from 23 April to 10 Jun) • 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 TIM, Alberto Oliva 21-25/ 07/2008 INFN / University of Perugia

Geometric Inefficiencies edges effect • Out of ladders hits • Out of sensor hits 1 mm Layer 2 1 mm • Sensitive area is reduced to a fiducial area due to “edges” effect (1 mm) TIM, Alberto Oliva 21-25/ 07/2008 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, Alberto Oliva 21-25/ 07/2008 INFN / University of Perugia

Signal Analysis (VI): Hit Correlation • Applying all the correction a unique gain is been achieved TIM, Alberto Oliva 21-25/ 07/2008 INFN / University of Perugia

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 (d x , d y , d z ) － Rotation (d x/ d y , d z/ d x , d z/ d y ) 3.5cm 30 ~ 60cm

Alignment iteration Before After

Alignment accuracy estimation Data divided into 5 samples (10 6 tracks each)

Alignment accuracy estimation Data divided into 5 samples (10 6 tracks each) Ladder alignment (X) σ ~2.0 μ m Ladder alignment (Y) σ ~2.2 μ m Statistical dependence: σ = p 0 + p 1 √ N

Cosmic-ray data analysis • Signal and noise check • Alignment study • Estimation of the position resolution

Multiple scattering and χ 2 cut MC simulation

Residual distributions (two - gaussian fit) σ 1 :narrow gaussian, σ 12 :weighted mean X Y: Bending direction Test beam Results

Resolution estimation with a simulation including multiple scattering

Resolution VS angle (Ladder average) X Y: Bending direction

Statistical dependece of resolution Statistical dependence: σ = p 0 + p 1 √ N X Y

Resolution VS SN ratio Vertical incidence X effective X optimal Y effective Y optimal

MDR estimated with MC • d R / R 2 is CR data porportinal to cos 3 θ 2.8 for 1/ L 2 cos 2 θ cos θ for σ Intrinsic 1.3 resolution Effective MC resolution Tracker Track L

AMS-02 potential for e + fraction AMS-02 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 (10 5 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 ( 2 σ ) Bergström et al . [arXiv:0905.0333] DM model : Nomura et al . [arXiv:0810.5397]

DM fit ( 2 σ ) – AMS - 02 expected Parameters assumed Bergström et al . [arXiv:0905.0333] DM model : Nomura et al . [arXiv:0810.5397]

AMS - 02 expected (ATIC － KKDM model)

Conclusions • Tracker performance estimated by CR muons • Stable and uniform signal and noise level • Alignment accuracy estimated as 2 μ m • Position resolution achieved as designed ( σ y = 10 μ m at θ ~ 0 ) agreed with Test Beam • Spillover limit estimated from measured resolution ~ 1 TeV for e + /e - separation