ion charge measurement with the ams-02 silicon tracker
DESCRIPTION
Ion charge measurement with the AMS-02 silicon tracker. 1rst Int. Workshop on High Energy cosmic-Radiation Detection October 17-18, 2012 IHEP CAS, Beijing. Martin Pohl, Pierre Saouter Center for Astroparticle Physics University of Geneva Alberto Oliva CIEMAT Madrid. - PowerPoint PPT PresentationTRANSCRIPT
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Ion charge measurementwith the AMS-02 silicon tracker
1rst Int. Workshop on High Energy cosmic-Radiation DetectionOctober 17-18, 2012IHEP CAS, Beijing
Martin Pohl, Pierre SaouterCenter for Astroparticle Physics
University of Geneva
Alberto OlivaCIEMAT Madrid
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Si Tracker Charge Measurement
Strip crosstalk
Gain (at VA level, using H, He and C)
Charge loss (position/angle dependence)
MIP scale conversion (saturation, non-linearities)
From ADC to energy deposition
Detector related corrections
From energy deposition to floating point charge estimators (Q)
From floating point chargeestimator to integer charge (Z)
Pathlength correction
Beta/Rigidity correction (layer dependent)
PDFZ(Edep)
Likelihood
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Si Tracker Charge Measurement
• Physics:
• From physics to ADC:• Si material properties• Nuclear charge: z2
• β and βγ: eV/μm• Path length in Si: dx• Ionisation yield: eV fC• Charge collection efficiency on strips• ASIC response function• Channel cross talk: ADC
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
The AMS Silicon Tracker
9 planes: 18 to 26 ladders Ladder : 7 to 15 double-sided silicon sensors. Implantation pitch p(n) side 27.5 (104) μm Readout pitch p(n) side 110 (208) μm (1/4 and 1/2 strips read out)
Ionization Energy Loss
• Signal usually collected by several adjacent strips (cluster)• Double threshold to eliminate insignificant strips
Cluster Amplitude
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
VA64hdr
Front-end electronics
10 VAs on the p-side (Y direction) 6 VAs on the n-side (X direction)
Each VA reads 64 channels
• Each VA produces a signal with different characteristics • In particular differences in the gain are observed• FEE response curve is deliberately non-linear, different for p and n
p-side
n-side
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Example of Gain Differences for He for p-side VAs of Ladder +307
Raw
AD
C
Typical ~10%, max ~35%
x 10
Helium Sample
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
• Landau function convoluted with a Gaussian• MPV to characterize the gain of a given VA
Single VA Distribution forProton.
Amplitude distribution (protons, single VA)
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Cluster pulse integral (single ladder) as function of ion charge
Alpat B. & al., 2004 (2003 Cern and GSI Test Beam)
Si
B
1. Two sides behave differently:• Maximum dynamic range• Good resolution at low charge
2. Two ~ linear response regimes
3. Same behavior expected for all VA
n side
p side
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Charge Calibration Sample Selection
• Uncalibrated charge response with rather good resolution• Define charge samples using truncated mean of hits on n side, corrected for impact angle • 1σ selection ranges around MPV
Avoid any bias in selection: • separate ranges for each layer • truncated mean excluding layer under study
• (see later)
HHe
LiBe
BC
NO
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
X-s
ide
Clu
ster
s
VA Number
• Proton• Helium• Carbon
Charge Calibration Sample Selection
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Reference MPV values for each charge
• Proton• Helium• Carbon
Readout Region
Individual VA gains equalized on reference value
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Good linearity of VA64 response
• Gain factor inde-pendent of particle impact location
• Small offset due to thresholds on seed and adjacent strips
Gain Corr. Fact
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Offset must be taken into accountin gain correction!
Gain Correction Factors and Offsets
At most 10% correctionneeded.
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Deviation of VA MPV values from Linear Fit
Systematic error ~ 3%
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Gain Correction Effect on H, He and C Samples
• No Correction• Gain Correction• Including Offsets
RMS improvesby factor of 3.5
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Gain Systematics
• Each point is mean of VA response per layer, with RMS as error• RMS is larger for layer 1• Systematics less than 0.5% << statistical error on gain factor
Layer 1 Layer 2 Layer 3 Layer 4 Layer 5 Layer 6 Layer 7 Layer 8 Layer 9
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Nu
mb
er
Nu
clei
C
BeB N
O
F
Ne
Na
MgSi
Li
He
HBefore CorrectionAfter Gain Corrections
Track Truncated Mean n Side
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
C
Be
BN
O
F
Ne
Na
Mg
Si
log
(N
um
ber
Nu
clei
) Before CorrectionAfter Gain Corrections
Zoom on High Charges n Side
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Resolution of Charge Estimator After Gain Correction
A. Oliva
• n side before correction• n side after gain correction
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Nu
mb
er
Nu
clei
C
BeB O
Ne
Li
He
H
Before CorrectionAfter Gain Corrections
Track Truncated Mean p Side
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Charge Collection Efficiency
Particle very near a readout strip.
Particle passes in between two readout strips.
Capacitive coupling between strips allows to estimate impact positionof the traversing particle (COG).
Charge loss ~30 % for Helium
0
Loss of collection efficiency in thenon-readout region
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Charge Collection: Impact Point and Angle
ZXZ Projected Track
θXZ
X
X
Y
Z
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Implant structure and n/p side differences
• n - side: 1 out of 2 strips read out + saturation• p - side: 1 out 4 strips readout + non linearity at low charges (B,C,O)
different charge collection behavior
Charge Loss For Carbon Sample
N-Side / Z=6 / ~28%P-Side / Z=6 / ~35%
ADC ADC
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Ne
O
C
B
Be N
F
• No Corr• Gain Corr• Gain + Charge Loss
Track Truncated Mean n Side
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Resolution of Charge Estimator After Correction
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
OC
Mg
FeSi
BBe
Li
Track Truncated Mean p Side
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Path Length Correction
Normalization to 300 μm of Silicon traversed.
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Beta Correction: Layer-by-Layer (II)
Z = 1 Z = 2
Z = 2 Z = 1 Layer 4 Layer 4
Layer 1Layer 1
Effect of TRD + upper TOF
Effect of TRD + upper TOF
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Beta Correction: Layer-by-Layer (III)
Z = 1 Z = 2
Z = 2 Z = 1 Layer 8Layer 8
Layer 9Layer 9
Effect of RICH + lower TOF
Effect of RICH + lower TOF
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Beta CorrectionProtons
Helium
TOF measures
β inside AMS
β > βTOF
βTOF
β < βTOF
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Tracker Charge Measurement
Z>10 should use p-side
n
Track Truncated Mean p–Side (c.u.)
Trac
k Tr
unca
ted
Mea
n n–
Sid
e (c
.u.)
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
MIP Correction • Transforms corrected response into charge units.• Accounts for saturation and non-linearity• Directly provided as an outcome of the charge loss correction
• Gives almost linear charge estimator• Some residual deviation left in the non-linearity regions
n side
p side
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
• Combine the n and p measurement with a weighted sum. • Weights depend on the number of hits used• Weights assumed to be independent of Z (approximately correct)
H x 10-3
He x 10-2
Be
C
O
Si
Fe
Joint Track Charge Estimator
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Going to PDF
1 23
45
6
78
9
1012
14
26
• This shapes should be understood in detail• Tails from wrong hit associated to tracks, interactions…• Specific ladder behavior • Dependencies on external parameters: t, T …
Layer 2 charge distributions
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
ZTRK_L1=6.1
ZTRD=5.9
ZTOF_UP=5.9
ZTOF_LOW=5.8
ZTRK_IN=5.8
ZRICH=6.1
Carbon: Rigidity=215 GV, P=1288 GeV, Ekin/A=106 GeV/n
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
ZTRK_L1=4.9
ZTRD=4.5
ZTOF_UP=5.0
ZTOF_LOW=5.1
ZTRK_IN=4.9
ZRICH=5.2
Boron: Rigidity=187 GV, P=935 GeV, Ekin/A=93 GeV/n
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Tracker and ToF
HHe
LiBe B
CN O
FNe
NaMg
AlSi
Cl Ar K Ca Sc Ti
V Cr
P SFe
Ni
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Martin Pohl
DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE
Conclusions• AMS Si tracker shows excellent nuclear charge
identification:– Excellent charge separation– Simple unfolding of species
• Complete calibration chain in place:– Floating point charge estimator– Probabilistic approach based on PDF
• Redundancy of subdetectors is key to systematic accuracy:– Tracker– ToF– RICH
• Chemical composition of cosmic rays GeV to TeV