Adding TRD in the combined PID (Yu.Belikov)
[u/mrichter/AliRoot.git] / TRD / AliTRDpidESD.cxx
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b0f03c34 1/**************************************************************************
2 * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
3 * *
4 * Author: The ALICE Off-line Project. *
5 * Contributors are mentioned in the code where appropriate. *
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7 * Permission to use, copy, modify and distribute this software and its *
8 * documentation strictly for non-commercial purposes is hereby granted *
9 * without fee, provided that the above copyright notice appears in all *
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11 * appear in the supporting documentation. The authors make no claims *
12 * about the suitability of this software for any purpose. It is *
13 * provided "as is" without express or implied warranty. *
14 **************************************************************************/
15
16//-----------------------------------------------------------------
17// Implementation of the TRD PID class
18// Very naive one... And the implementation is even poorer...
19// Should be made better by the detector experts...
20//-----------------------------------------------------------------
21
22#include "AliTRDpidESD.h"
23#include "AliESD.h"
24#include "AliESDtrack.h"
25
26ClassImp(AliTRDpidESD)
27
28//_________________________________________________________________________
29AliTRDpidESD::AliTRDpidESD(Double_t *param)
30{
31 //
32 // The main constructor
33 //
34 fMIP=param[0]; // MIP signal
35 fRes=param[1]; // relative resolution
36 fRange=param[2]; // PID "range" (in sigmas)
37}
38
39Double_t AliTRDpidESD::Bethe(Double_t bg) {
40 //
41 // This is the Bethe-Bloch function normalised to 1 at the minimum
42 //
43 Double_t bg2=bg*bg;
44 Double_t bethe;
45 if (bg<3.5e1)
46 bethe=(1.+ bg2)/bg2*(log(5940*bg2) - bg2/(1.+ bg2));
47 else // Density effect ( approximately :)
48 bethe=(1.+ bg2)/bg2*(log(3.5*5940*bg) - bg2/(1.+ bg2));
49 return bethe/11.091;
50}
51
52//_________________________________________________________________________
53Int_t AliTRDpidESD::MakePID(AliESD *event)
54{
55 //
56 // This function calculates the "detector response" PID probabilities
57 //
58 static const Double_t masses[]={
59 0.000511, 0.105658, 0.139570, 0.493677, 0.938272, 1.875613
60 };
61 Int_t ntrk=event->GetNumberOfTracks();
62 for (Int_t i=0; i<ntrk; i++) {
63 AliESDtrack *t=event->GetTrack(i);
64 if ((t->GetStatus()&AliESDtrack::kTRDin)==0)
65 if ((t->GetStatus()&AliESDtrack::kTRDout)==0)
66 if ((t->GetStatus()&AliESDtrack::kTRDrefit)==0) continue;
67 Int_t ns=AliESDtrack::kSPECIES;
68 Double_t p[10];
69 for (Int_t j=0; j<ns; j++) {
70 Double_t mass=masses[j];
71 Double_t mom=t->GetP();
72 Double_t dedx=t->GetTRDsignal()/fMIP;
73 Double_t bethe=Bethe(mom/mass);
74 Double_t sigma=fRes*bethe;
75 if (TMath::Abs(dedx-bethe) > fRange*sigma) {
76 p[j]=TMath::Exp(-0.5*fRange*fRange)/sigma;
77 continue;
78 }
79 p[j]=TMath::Exp(-0.5*(dedx-bethe)*(dedx-bethe)/(sigma*sigma))/sigma;
80 }
81 t->SetTRDpid(p);
82 }
83 return 0;
84}