Page 1 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE 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

Page 2 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 charge estimator to integer charge (Z) Pathlength correction Beta/Rigidity correction (layer dependent) PDF Z (E dep ) Likelihood

Page 3 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Si Tracker Charge Measurement Physics: Physics: From physics to ADC: From physics to ADC: Si material properties Si material properties Nuclear charge:z 2 Nuclear charge:z 2 β and βγ:eV/μm β and βγ:eV/μm Path length in Si:dx Path length in Si:dx Ionisation yield: eV  fC Ionisation yield: eV  fC Charge collection efficiency on strips Charge collection efficiency on strips ASIC response function ASIC response function Channel cross talk: ADC Channel cross talk: ADC

Page 4 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) Signal usually collected by several adjacent strips (cluster) Double threshold to eliminate insignificant strips Double threshold to eliminate insignificant strips Cluster Amplitude

Page 5 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 Each VA produces a signal with different characteristics In particular differences in the gain are observed In particular differences in the gain are observed FEE response curve is deliberately non-linear, different for p and n FEE response curve is deliberately non-linear, different for p and n p-side n-side

Page 6 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Example of Gain Differences for He for p-side VAs of Ladder +307 Raw ADC Typical ~10%, max ~35% x 10 Helium Sample

Page 7 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Landau function convoluted with a Gaussian Landau function convoluted with a Gaussian MPV to characterize the gain of a given VA MPV to characterize the gain of a given VA Single VA Distribution for Proton. Amplitude distribution (protons, single VA)

Page 8 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 rangeMaximum dynamic range Good resolution at low chargeGood resolution at low charge 2.Two ~ linear response regimes 3.Same behavior expected for all VA n side p side

Page 9 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Charge Calibration Sample Selection Uncalibrated charge response with rather good resolution Uncalibrated charge response with rather good resolution Define charge samples using truncated mean of hits on n side, corrected for impact angle Define charge samples using truncated mean of hits on n side, corrected for impact angle 1σ selection ranges around MPV 1σ selection ranges around MPV Avoid any bias in selection: separate ranges for each layer separate ranges for each layer truncated mean excluding layer under study truncated mean excluding layer under study (see later) (see later) H He Li Be B C N O

Page 10 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE X-side Clusters VA Number Proton Helium Carbon Charge Calibration Sample Selection

Page 11 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Reference MPV values for each charge ProtonProton HeliumHelium CarbonCarbon Readout Region Individual VA gains equalized on reference value

Page 12 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Good linearity of VA64 response Gain factor inde- pendent of particle impact location Gain factor inde- pendent of particle impact location Small offset due to thresholds on seed and adjacent strips Small offset due to thresholds on seed and adjacent strips Gain Corr. Fact

Page 13 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Offset must be taken into account in gain correction! Gain Correction Factors and Offsets At most 10% correction needed.

Page 14 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Deviation of VA MPV values from Linear Fit Systematic error ~ 3%

Page 15 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Gain Correction Effect on H, He and C Samples No Correction Gain Correction Including Offsets RMS improves by factor of 3.5

Page 16 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Gain Systematics Each point is mean of VA response per layer, with RMS as errorEach point is mean of VA response per layer, with RMS as error RMS is larger for layer 1RMS is larger for layer 1 Systematics less than 0.5% << statistical error on gain factorSystematics 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

Page 17 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Number Nuclei C Be B N O F Ne Na Mg Si Li He H Before Correction After Gain Corrections Track Truncated Mean n Side

Page 18 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE C Be B N O F Ne Na Mg Si log (Number Nuclei) Before Correction After Gain Corrections Zoom on High Charges n Side

Page 19 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

Page 20 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Number Nuclei C Be B O Ne Li He H Before Correction After Gain Corrections Track Truncated Mean p Side

Page 21 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 position of the traversing particle (COG). Charge loss ~30 % for Helium 00 Loss of collection efficiency in the non-readout region

Page 22 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Charge Collection: Impact Point and Angle Z XZ Projected Track θ XZ X X Y Z

Page 23 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

Page 24 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

Page 25 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Resolution of Charge Estimator After Correction

Page 26 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE O C Mg Fe Si B Be Li Track Truncated Mean p Side

Page 27 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Path Length Correction Normalization to 300 μm of Silicon traversed.

Page 28 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Beta Correction: Layer-by-Layer (II) Z = 1 Z = 2 Z = 1 Layer 4 Layer 1 Effect of TRD + upper TOF Effect of TRD + upper TOF

Page 29 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Beta Correction: Layer-by-Layer (III) Z = 1 Z = 2 Z = 1 Layer 8 Layer 9 Effect of RICH + lower TOF Effect of RICH + lower TOF

Page 30 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Beta Correction Protons Helium TOF measures β inside AMS β > β TOF β TOF β < β TOF

Page 31 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.) Track Truncated Mean n–Side (c.u.)

Page 32 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE MIP Correction MIP Correction Transforms corrected response into charge units. Transforms corrected response into charge units. Accounts for saturation and non-linearity Accounts for saturation and non-linearity Directly provided as an outcome of the charge loss correction Directly provided as an outcome of the charge loss correction Gives almost linear charge estimator Gives almost linear charge estimator Some residual deviation left in the non-linearity regions Some residual deviation left in the non-linearity regions n side p side

Page 33 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Combine the n and p measurement with a weighted sum.Combine the n and p measurement with a weighted sum. Weights depend on the number of hits usedWeights depend on the number of hits used Weights assumed to be independent of Z (approximately correct)Weights assumed to be independent of Z (approximately correct) H x He x Be C O Si Fe Joint Track Charge Estimator Joint Track Charge Estimator

Page 34 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Going to PDF 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

Page 35 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Z TRK_L1 =6.1 Z TRD =5.9 Z TOF_UP =5.9 Z TOF_LOW =5.8 Z TRK_IN =5.8 Z RICH =6.1 Carbon: Rigidity=215 GV, P=1288 GeV, E kin /A=106 GeV/n

Page 36 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Z TRK_L1 =4.9 Z TRD =4.5 Z TOF_UP =5.0 Z TOF_LOW =5.1 Z TRK_IN =4.9 Z RICH =5.2 Boron: Rigidity=187 GV, P=935 GeV, E kin /A=93 GeV/n

Page 37 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Tracker and ToF H He Li Be B C NO F Ne Na Mg Al Si ClAr K Ca ScTi V Cr P S Fe Ni

Page 38 Martin Pohl DEPARTEMENT DE PHYSIQUE NUCLEAIRE ET CORPUSCULAIRE Conclusions AMS Si tracker shows excellent nuclear charge identification:AMS Si tracker shows excellent nuclear charge identification: –Excellent charge separation –Simple unfolding of species Complete calibration chain in place:Complete calibration chain in place: –Floating point charge estimator –Probabilistic approach based on PDF Redundancy of subdetectors is key to systematic accuracy:Redundancy of subdetectors is key to systematic accuracy: –Tracker –ToF –RICH Chemical composition of cosmic rays GeV to TeVChemical composition of cosmic rays GeV to TeV