inner tracking system pidpersonalpages.to.infn.it/~biolcati/itspid.pdf · 2009-07-01 · de/dx...
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Inner Tracking System PID
Emanuele Biolcati (Università and INFN Torino)
Marek Chojnacki (Universiteit Utrecht)
PID task force meeting – July 2, 2009
2-7-2009 Biolcati & Chojnacki - PID in ITS 2
Outlines
Introduction: two PID algorithms for the ITS
PID 1
Performance (PDC09)
Real life PID in SSD
PID 2
Upgrade in the code
Status
SDD features
Conclusions
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Two PID algorithms
SDD+SSDpoints
Calculation of the fITSsignal (dE), mean truncated of points charges.
AliITSpidESD1 class
AliITSpidESD2 class
fITSsignal andpoints
only fITSsignal
fITSsignal (dE) is stored in ESD
PID stored in ESD
During the reconstruction, with AliITSRecoparam() it is possible to choose:
AliITSpidESD1
AliITSpidESD2
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PID 1
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ITS signal in PDC09 (PID1)
Theoretical values of dE according to the AliESDpidESD class
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PID1 cuts
Proton = track with probability of being proton>0.5
Kaon = track with probability of being Kaon>0.5
Pion = track with probability of being pion or muon>0.5 if (p<250MeV/c) and track with probability of being pion or muon or electron >0.5 if (p>250MeV/c,p<900MeV/c)
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Test of PID1 cuts in PDC09.Efficiency , K,p
Purity , K,pNS(i)=number of selected tracks assigned to be particle type“i”
NR(i)=number of reconstructible tracks made by particles type “i”
NMCS(i)=number of selected tracks which were made by particle type “i”
efficiency i =NS i
NRi
purity i =NMCS i
NS i
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Based on PDC09. What can we do?
PID1 in the ITS allows to recognize : ● up to p=800MeV/c
● K up to p=800MeV/c
● P= up to p=1.3GeV/c
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SSD calibration
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Real life PID1 in SSD
Cosmic tracks taken with the field on, only SSD information on dE.
Theoretical values of dE according to the AliESDpidESD class
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PID 2
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PID2 algorithm
● Event generation (PYTHIA or HIJING)
● Tracking in ITS (tracks with 4 clusters in SDD and SSD)
● For each reconstructed track, all the 4 charge signals coming from the 4 different layers (SDD+SSD) retrieved
● dE/dx histograms in momentum slices 0.032 GeV/c wide
● For each momentum bin, dE/dx distribution for protons, kaons, pions (R(S)) fitted by LandauGaussian convolution
● Fit parameters plotted versus momentum bins and fitted by ad hoc functions f
i(p)
● Bayesian approach using a recursive method
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PID2: binning in momentum
● For each particle specie, for each layer (SDD and SSD), binning in momentum is performed
● 50 bins 32 MeV/c wide, from 0 to 1.6 GeV
● Fit parameters are stored to be plotted versus momentum
Examplelayer 3particle π640 MeV < P < 672 MeV
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PID2 upgrades• Feature in the old code:
• Bug: track not propagated to the module plane before extracting the angles used for track length normalization in AliITSpidESD2
• Limitation: charge for PID2 extracted from RecPoints and not stored in ESD track, so it was not possible to run PID2 starting from ESD
• Solution implemented in aliroot trunk since rev. 32870• 4 samples of ITS dE/dx stored in AliESDtrack with truncated mantissa
(Belikov)
pidESD2 does not need RecPoints, can be run on ESD
• Correction for track length in detector plane managed in the trackers (via AliITStrackV2::SetSampledEdx) also for PID
New, for all trackers (MI, SA, V2) the 4 samples are stored ordered by layer, from SDD inner [0] to SSD outer [3]
Signal from extra clusters not stored in ESD tracks
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Cross check for the angle
From AliITStrackV2.h:inline void AliITStrackV2::SetSampledEdx(Float_t q, Int_t i){ if (i<0) return; if (i>3) return; Double_t s=GetSnp(), t=GetTgl(); q *= TMath::Sqrt((1s*s)/(1+t*t)); fdEdxSample[i]=q; return;}
Angle calculate after the track propagation on the ITS modules
Savannah#50855
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Signal of 4 clusters onlyNo extraclusters
• The effect of extraclusters will be studied on MonteCarlo samples starting from RecPoints
• If their contribute will result to be important, a revision of the code will be performed
• E.g. from AliITSTrackV2.cxx:
void AliITStrackV2::CookdEdx(Double_t low, Double_t up) { // The cluster order is: SDD1, SDD2, SSD1, SSD2
Int_t nc=0; Float_t dedx[4]; for (Int_t il=0; il<4; il++) { if(fdEdxSample[il]>0.){ dedx[nc]= fdEdxSample[il]; nc++; } } if(nc<1){ SetdEdx(0.); return; }
Different order, from SDD to SSD
Only 4 cluster,no extra-clusters
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SDD: zerosuppression effect
• Electron cloud, generated in the Si, spreads during the drift
• Signal tails could be cut by the zerosuppression algorithm
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SDD: correction for zero suppression
From AliITSresponseSDD.cxx
From AliITSClusterFinderV2SDD.cxx
const Float_t AliITSresponseSDD::fgkADC2keVDefault = 3.34;const Float_t AliITSresponseSDD::fgkChargevsTimeDefault = 0.00355;
q/=rsdd>GetADC2keV(); q+=(driftTime*rsdd>GetChargevsTime());
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PID2 response functions
Layer 3 (SDD), pions, pp event
Preliminary results(few statistics with last update)
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CONCLUSIONS
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Conclusions (PID)
PID1
quite good performance in the PDC09
update of the code allows to “play” with this method during analysis of ESDs
PID2
work in progress to retune the response functions
no major development on the code needed
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Conclusions (calibration)
SSD
It looks that calibration is ok up to level of few %.
We are developing code for more precise calibration.
SDD
Zero suppression correction now included
ADC to keV fine tuned up to level of few %
Cross check on the corrections performed
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Backup
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Simulation for zero suppression (SDD)
Effect due to the detector discretization
From a simulation: