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[u/mrichter/AliRoot.git] / TRD / AliTRDpidESD.cxx

/**************************************************************************
 * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
 *                                                                        *
 * Author: The ALICE Off-line Project.                                    *
 * Contributors are mentioned in the code where appropriate.              *
 *                                                                        *
 * Permission to use, copy, modify and distribute this software and its   *
 * documentation strictly for non-commercial purposes is hereby granted   *
 * without fee, provided that the above copyright notice appears in all   *
 * copies and that both the copyright notice and this permission notice   *
 * appear in the supporting documentation. The authors make no claims     *
 * about the suitability of this software for any purpose. It is          *
 * provided "as is" without express or implied warranty.                  *
 **************************************************************************/

/* $Id$ */

////////////////////////////////////////////////////////////////////////////
//                                                                        //
// Implementation of the TRD PID class                                    //
//                                                                        //
// Assigns the electron and pion likelihoods to each ESD track.           //
// The function MakePID(AliESDEvent *event) calculates the probability    //
// of having dedx and a maximum timbin at a given                         //
// momentum (mom) and particle type k                                     //
// from the precalculated distributions.                                  //
//                                                                        //
// Authors :                                                              //
//   Prashant Shukla <shukla@pi0.physi.uni-heidelberg.de> (orig. version) //
//   Alex Bercuci (a.bercuci@gsi.de)                                      //
//                                                                        //
////////////////////////////////////////////////////////////////////////////

#include "AliLog.h"
#include "AliESDEvent.h"
#include "AliESDtrack.h"
#include "AliTracker.h"
#include "AliRun.h"

#include "AliTRDpidESD.h"
#include "AliTRDgeometry.h"
#include "AliTRDcalibDB.h"
#include "AliTRDtrack.h"
#include "Cal/AliTRDCalPID.h"

ClassImp(AliTRDpidESD)

Bool_t  AliTRDpidESD::fgCheckTrackStatus = kTRUE;
Bool_t  AliTRDpidESD::fgCheckKinkStatus  = kFALSE;
Int_t   AliTRDpidESD::fgMinPlane         = 0;

//_____________________________________________________________________________
AliTRDpidESD::AliTRDpidESD()
  :TObject()
  ,fTrack(0x0)
{
  //
  // Default constructor
  //

}

//_____________________________________________________________________________
AliTRDpidESD::AliTRDpidESD(const AliTRDpidESD &p)
  :TObject(p)
  ,fTrack(0x0)
{
  //
  // AliTRDpidESD copy constructor
  //

  ((AliTRDpidESD &) p).Copy(*this);

}

//_____________________________________________________________________________
AliTRDpidESD::~AliTRDpidESD()
{
  //
  // Destructor
  //

  if(fTrack) delete fTrack;

}

//_____________________________________________________________________________
AliTRDpidESD &AliTRDpidESD::operator=(const AliTRDpidESD &p)
{
  //
  // Assignment operator
  //

  if (this != &p) ((AliTRDpidESD &) p).Copy(*this);
  return *this;

}

//_____________________________________________________________________________
void AliTRDpidESD::Copy(TObject &p) const
{
  //
  // Copy function
  //

  ((AliTRDpidESD &) p).fgCheckTrackStatus         = fgCheckTrackStatus;
  ((AliTRDpidESD &) p).fgCheckKinkStatus          = fgCheckKinkStatus;
  ((AliTRDpidESD &) p).fgMinPlane                 = fgMinPlane;
  ((AliTRDpidESD &) p).fTrack                     = 0x0;
	
}

//_____________________________________________________________________________
Int_t AliTRDpidESD::MakePID(AliESDEvent *event)
{
  //
  // This function calculates the PID probabilities based on TRD signals
  //
  // The method produces probabilities based on the charge
  // and the position of the maximum time bin in each layer.
  // The dE/dx information can be used as global charge or 2 to 3
  // slices. Check AliTRDCalPID and AliTRDCalPIDRefMaker for the actual
  // implementation.
  //
  // Author
  // Alex Bercuci (A.Bercuci@gsi.de) 2nd May 2007
  //

	AliTRDcalibDB *calibration = AliTRDcalibDB::Instance();
	if (!calibration) {
		AliErrorGeneral("AliTRDpidESD::MakePID()"
			,"No access to calibration data");
		return -1;
	}
	
	// Retrieve the CDB container class with the probability distributions
	const AliTRDCalPID *pd = calibration->GetPIDObject(1);
	if (!pd) {
		AliErrorGeneral("AliTRDpidESD::MakePID()"
			,"No access to AliTRDCalPID");
		return -1;
	}

	// Loop through all ESD tracks
	Double_t p[10];
	AliESDtrack *t = 0x0;
	Float_t dedx[AliTRDtrack::kNslice], dEdx;
	Int_t   timebin;
	Float_t mom, length;
	Int_t   nPlanePID;
	for (Int_t i=0; i<event->GetNumberOfTracks(); i++) {
		t = event->GetTrack(i);
		
		// Check track
		if(!CheckTrack(t)) continue;

						
		// Skip tracks which have no TRD signal at all
		if (t->GetTRDsignal() == 0.) continue;
	
		// Loop over detector layers
		mom          = 0.;
		length       = 0.;
		nPlanePID    = 0;
		for (Int_t iSpecies = 0; iSpecies < AliPID::kSPECIES; iSpecies++) 
                  p[iSpecies] = 1./AliPID::kSPECIES;

		for (Int_t iPlan = 0; iPlan < AliTRDgeometry::kNplan; iPlan++) {
			// read data for track segment
			for(int iSlice=0; iSlice<AliTRDtrack::kNslice; iSlice++)
				dedx[iSlice] = t->GetTRDsignals(iPlan, iSlice);
			dEdx    = t->GetTRDsignals(iPlan, -1);
			timebin = t->GetTRDTimBin(iPlan);

			// check data
			if ((dEdx <=  0.) || (timebin <= -1.)) continue;

			// retrive kinematic info for this track segment
			if(!RecalculateTrackSegmentKine(t, iPlan, mom, length)){
				// information is not fully reliable especialy for length
				// estimation. To be used in the future. 
			}
			
			// this track segment has fulfilled all requierments
			nPlanePID++;

			// Get the probabilities for the different particle species
			for (Int_t iSpecies = 0; iSpecies < AliPID::kSPECIES; iSpecies++) {
				p[iSpecies] *= pd->GetProbability(iSpecies, mom, dedx, length, iPlan);
				//p[iSpecies] *= pd->GetProbabilityT(iSpecies, mom, timebin);
			}
		}
		if(nPlanePID == 0) continue;
		
		// normalize probabilities
		Double_t probTotal = 0.;
		for (Int_t iSpecies = 0; iSpecies < AliPID::kSPECIES; iSpecies++) probTotal   += p[iSpecies];
		if(probTotal <= 0.){
			AliWarning(Form("The total probability (%e) over all species <= 0 in ESD track %d."
                                       , probTotal, i));
			AliWarning("This may be caused by some error in reference data.");
			AliWarning("Calculation continues but results might be corrupted.");
			continue;
		}
		for(Int_t iSpecies = 0; iSpecies < AliPID::kSPECIES; iSpecies++) p[iSpecies] /= probTotal;

		// book PID to the track
		t->SetTRDpid(p);
		t->SetTRDpidQuality(nPlanePID);
	}
	
	return 0;

}

//_____________________________________________________________________________
Bool_t AliTRDpidESD::CheckTrack(AliESDtrack *t)
{
  //
  // Check if track is eligible for PID calculations
  //
	
	// Check the ESD track status
	if (fgCheckTrackStatus) {
		if (((t->GetStatus() & AliESDtrack::kTRDout  ) == 0) &&
			((t->GetStatus() & AliESDtrack::kTRDrefit) == 0)) return kFALSE;
	}

	// Check for ESD kink tracks
	if (fgCheckKinkStatus && (t->GetKinkIndex(0) != 0)) return kFALSE;

	return kTRUE;

}

//_____________________________________________________________________________
Bool_t AliTRDpidESD::RecalculateTrackSegmentKine(AliESDtrack *esd
                                               , Int_t plan
                                               , Float_t &mom
                                               , Float_t &length)
{
  //
  // Retrive momentum "mom" and track "length" in TRD chamber from plane
  // "plan" according to information stored in AliESDtrack "t".
  //
  // Origin
  // Alex Bercuci (A.Bercuci@gsi.de)	
  //

	const Float_t kAmHalfWidth = AliTRDgeometry::AmThick() / 2.;
        const Float_t kDrWidth     = AliTRDgeometry::DrThick();
	const Float_t kTime0       = AliTRDgeometry::GetTime0(plan);

	// set initial length value to chamber height 
	length = 2 * kAmHalfWidth + kDrWidth;
		
	// retrive track's outer param
	const AliExternalTrackParam *op = esd->GetOuterParam();
	if(!op){
		mom    = esd->GetP();
		return kFALSE;
	}

	AliExternalTrackParam *param = 0x0;
	if(!fTrack){
		fTrack = new AliExternalTrackParam(*op);
		param = fTrack;
	} else param = new(fTrack) AliExternalTrackParam(*op);
	
	// retrive the magnetic field
	Double_t xyz0[3];
	op->GetXYZ(xyz0);
	Float_t field = AliTracker::GetBz(xyz0); // Bz in kG at point xyz0
	Double_t s, t;

	// propagate to chamber entrance
	if(!param->PropagateTo(kTime0-kAmHalfWidth-kDrWidth, field)){
		mom    = op->GetP();
		s      = op->GetSnp();
		t      = op->GetTgl();
	        if (s < 1.) length /= TMath::Sqrt((1. - s*s) / (1. + t*t));
		return kFALSE;
	}
	mom        = param->GetP();
	s = param->GetSnp();
	t = param->GetTgl();
	if (s < 1.) length    /= TMath::Sqrt((1. - s*s) / (1. + t*t));

	// check if track is crossing tracking sector by propagating to chamber exit- maybe is too much :)
	Double_t alpha = param->GetAlpha();
	if(!param->PropagateTo(kTime0+kAmHalfWidth, field)) return kFALSE;
		
	// mark track segments which are crossing SM boundaries along chamber
	if(TMath::Abs(alpha-param->GetAlpha())>.01) return kFALSE;
	
	return kTRUE;

}