From ed268b64c3a3d1c1bc403015e8d618ed747da47c Mon Sep 17 00:00:00 2001
From: morsch <andreas.morsch@cern.ch>
Date: Fri, 7 Mar 2014 22:02:15 +0100
Subject: [PATCH] This is a protection against the case "label 0 tracks" in MC
 Pietro Antonioli

---
 STEER/AOD/AliAODpidUtil.cxx | 43 +++++++++++++++++---------------
 STEER/ESD/AliESDpid.cxx     | 49 +++++++++++++++++++------------------
 2 files changed, 48 insertions(+), 44 deletions(-)

diff --git a/STEER/AOD/AliAODpidUtil.cxx b/STEER/AOD/AliAODpidUtil.cxx
index 4c61bb46bd5..f7c41b06cce 100644
--- a/STEER/AOD/AliAODpidUtil.cxx
+++ b/STEER/AOD/AliAODpidUtil.cxx
@@ -55,40 +55,43 @@ Float_t AliAODpidUtil::GetTPCsignalTunedOnData(const AliVTrack *t) const {
     
     AliAODMCHeader *mcHeader = dynamic_cast<AliAODMCHeader*>(track->GetAODEvent()->GetList()->FindObject(AliAODMCHeader::StdBranchName()));
     if (mcHeader) {
+        
 	TClonesArray *mcArray = (TClonesArray*)track->GetAODEvent()->GetList()->FindObject(AliAODMCParticle::StdBranchName());
 	
 	Bool_t kGood = kTRUE;
-	
-	Int_t iS = TMath::Abs(((AliAODMCParticle*)mcArray->At(TMath::Abs(t->GetLabel())))->GetPdgCode());
-	if(iS==AliPID::ParticleCode(AliPID::kElectron)){
+
+	if ( mcArray->At(TMath::Abs(t->GetLabel())) != NULL ) {  // protects against label-0 tracks e.g. the initial proton for Phythia events
+	  Int_t iS = TMath::Abs(((AliAODMCParticle*)mcArray->At(TMath::Abs(t->GetLabel())))->GetPdgCode());
+	  if(iS==AliPID::ParticleCode(AliPID::kElectron)){
 	    type = AliPID::kElectron;
-	}
-	else if(iS==AliPID::ParticleCode(AliPID::kMuon)){
+	  }
+	  else if(iS==AliPID::ParticleCode(AliPID::kMuon)){
 	    type = AliPID::kMuon;
-	}
-	else if(iS==AliPID::ParticleCode(AliPID::kPion)){
+	  }
+	  else if(iS==AliPID::ParticleCode(AliPID::kPion)){
 	    type = AliPID::kPion;
-	}
-	else if(iS==AliPID::ParticleCode(AliPID::kKaon)){
+	  }
+	  else if(iS==AliPID::ParticleCode(AliPID::kKaon)){
 	    type = AliPID::kKaon;
-	}
-	else if(iS==AliPID::ParticleCode(AliPID::kProton)){
+	  }
+	  else if(iS==AliPID::ParticleCode(AliPID::kProton)){
 	    type = AliPID::kProton;
-	}
-	else if(iS==AliPID::ParticleCode(AliPID::kDeuteron)){ // d
+	  }
+	  else if(iS==AliPID::ParticleCode(AliPID::kDeuteron)){ // d
 	    type = AliPID::kDeuteron;
-	}
-	else if(iS==AliPID::ParticleCode(AliPID::kTriton)){ // t
+	  }
+	  else if(iS==AliPID::ParticleCode(AliPID::kTriton)){ // t
 	    type = AliPID::kTriton;
-	}
-	else if(iS==AliPID::ParticleCode(AliPID::kHe3)){ // 3He
+	  }
+	  else if(iS==AliPID::ParticleCode(AliPID::kHe3)){ // 3He
 	    type = AliPID::kHe3;
-	}
-	else if(iS==AliPID::ParticleCode(AliPID::kAlpha)){ // 4He
+	  }
+	  else if(iS==AliPID::ParticleCode(AliPID::kAlpha)){ // 4He
 	    type = AliPID::kAlpha;
-	}
+	  }
 	else
 	    kGood = kFALSE;
+	} else kGood = kFALSE;
 
 	if(kGood){
 	    //TODO maybe introduce different dEdxSources?
diff --git a/STEER/ESD/AliESDpid.cxx b/STEER/ESD/AliESDpid.cxx
index 88a23dc2523..f62b3a30c70 100644
--- a/STEER/ESD/AliESDpid.cxx
+++ b/STEER/ESD/AliESDpid.cxx
@@ -88,40 +88,41 @@ Float_t AliESDpid::GetTPCsignalTunedOnData(const AliVTrack *t) const {
 	if(mcEvent){
 	    Bool_t kGood = kTRUE;
 	    AliMCParticle *MCpart = (AliMCParticle *) mcEvent->GetTrack(TMath::Abs(t->GetLabel()));
-	    TParticle *part = MCpart->Particle();
-	    
-	    Int_t iS = TMath::Abs(part->GetPdgCode());
-
-	    if(iS==AliPID::ParticleCode(AliPID::kElectron)){
+	    if (MCpart != NULL) { // protect against label-0 track (initial proton in Pythia events)
+	      TParticle *part = MCpart->Particle(); 
+	      Int_t iS = TMath::Abs(part->GetPdgCode());
+	      
+	      if(iS==AliPID::ParticleCode(AliPID::kElectron)){
 		type = AliPID::kElectron;
-	    }
-	    else if(iS==AliPID::ParticleCode(AliPID::kMuon)){
+	      }
+	      else if(iS==AliPID::ParticleCode(AliPID::kMuon)){
 		type = AliPID::kMuon;
-	    }
-	    else if(iS==AliPID::ParticleCode(AliPID::kPion)){
+	      }
+	      else if(iS==AliPID::ParticleCode(AliPID::kPion)){
 		type = AliPID::kPion;
-	    }
-	    else if(iS==AliPID::ParticleCode(AliPID::kKaon)){
+	      }
+	      else if(iS==AliPID::ParticleCode(AliPID::kKaon)){
 		type = AliPID::kKaon;
-	    }
-	    else if(iS==AliPID::ParticleCode(AliPID::kProton)){
+	      }
+	      else if(iS==AliPID::ParticleCode(AliPID::kProton)){
 		type = AliPID::kProton;
-	    }
-	    else if(iS==AliPID::ParticleCode(AliPID::kDeuteron)){ // d
+	      }
+	      else if(iS==AliPID::ParticleCode(AliPID::kDeuteron)){ // d
 		type = AliPID::kDeuteron;
-	    }
-	    else if(iS==AliPID::ParticleCode(AliPID::kTriton)){ // t
+	      }
+	      else if(iS==AliPID::ParticleCode(AliPID::kTriton)){ // t
 		type = AliPID::kTriton;
-	    }
-	    else if(iS==AliPID::ParticleCode(AliPID::kHe3)){ // 3He
+	      }
+	      else if(iS==AliPID::ParticleCode(AliPID::kHe3)){ // 3He
 		type = AliPID::kHe3;
-	    }
-	    else if(iS==AliPID::ParticleCode(AliPID::kAlpha)){ // 4He
+	      }
+	      else if(iS==AliPID::ParticleCode(AliPID::kAlpha)){ // 4He
 		type = AliPID::kAlpha;
-	    }
-	    else
+	      }
+	      else
 		kGood = kFALSE;
-
+	    } else kGood = kFALSE;
+	    
 	    if(kGood){
         //TODO maybe introduce different dEdxSources?
         Double_t bethe = fTPCResponse.GetExpectedSignal(track, type, AliTPCPIDResponse::kdEdxDefault, this->UseTPCEtaCorrection(),
-- 
2.39.3