AliCascadeVertexer.cxx

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//-------------------------------------------------------------------------
//               Implementation of the cascade vertexer class
//          Reads V0s and tracks, writes out cascade vertices
//                     Fills the ESD with the cascades 
//    Origin: Christian Kuhn, IReS, Strasbourg, christian.kuhn@ires.in2p3.fr
//-------------------------------------------------------------------------

//modified by R. Vernet 30/6/2006 : daughter label
//modified by R. Vernet  3/7/2006 : causality
//modified by I. Belikov 24/11/2006 : static setter for the default cuts

#include "AliESDEvent.h"
#include "AliESDcascade.h"
#include "AliCascadeVertexer.h"

ClassImp(AliCascadeVertexer)

//A set of loose cuts
Double_t 
  AliCascadeVertexer::fgChi2max=33.;   //maximal allowed chi2 
Double_t 
  AliCascadeVertexer::fgDV0min=0.01;   //min V0 impact parameter
Double_t 
  AliCascadeVertexer::fgMassWin=0.008; //"window" around the Lambda mass
Double_t 
  AliCascadeVertexer::fgDBachMin=0.01; //min bachelor impact parameter
Double_t 
  AliCascadeVertexer::fgDCAmax=2.0;    //max DCA between the V0 and the track 
Double_t 
  AliCascadeVertexer::fgCPAmin=0.98; //min cosine of the cascade pointing angle
Double_t 
  AliCascadeVertexer::fgRmin=0.2;      //min radius of the fiducial volume
Double_t 
  AliCascadeVertexer::fgRmax=100.;     //max radius of the fiducial volume
  

Int_t AliCascadeVertexer::V0sTracks2CascadeVertices(AliESDEvent *event) {
  //--------------------------------------------------------------------
  // This function reconstructs cascade vertices
  //      Adapted to the ESD by I.Belikov (Jouri.Belikov@cern.ch)
  //--------------------------------------------------------------------
   const AliESDVertex *vtxT3D=event->GetPrimaryVertex();

   Double_t xPrimaryVertex=vtxT3D->GetX();
   Double_t yPrimaryVertex=vtxT3D->GetY();
   Double_t zPrimaryVertex=vtxT3D->GetZ();

   Double_t b=event->GetMagneticField();
   Int_t nV0=(Int_t)event->GetNumberOfV0s();

   //stores relevant V0s in an array
   TObjArray vtcs(nV0);
   Int_t i;
   for (i=0; i<nV0; i++) {
       AliESDv0 *v=event->GetV0(i);
       if (v->GetOnFlyStatus()) continue;
       if (v->GetD(xPrimaryVertex,yPrimaryVertex,zPrimaryVertex)<fDV0min) continue;
       vtcs.AddLast(v);
   }
   nV0=vtcs.GetEntriesFast();

   // stores relevant tracks in another array
   Int_t nentr=(Int_t)event->GetNumberOfTracks();
   int trk[nentr], ntr=0;
   for (i=0; i<nentr; i++) {
     AliESDtrack *esdtr=event->GetTrack(i);
     ULong_t status=esdtr->GetStatus();
     if (status&AliESDtrack::kITSpureSA) continue;
     if ((status&AliESDtrack::kITSrefit)==0)
       if ((status&AliESDtrack::kTPCrefit)==0) continue;

       if (TMath::Abs(esdtr->GetD(xPrimaryVertex,yPrimaryVertex,b))<fDBachMin) continue;

       trk[ntr++]=i;
   }   

   Double_t massLambda=1.11568;
   Int_t ncasc=0;

   // Looking for the cascades...

   for (i=0; i<nV0; i++) { //loop on V0s

      AliESDv0 *v=(AliESDv0*)vtcs.UncheckedAt(i);
      AliESDv0 v0(*v);
      v0.ChangeMassHypothesis(kLambda0); // the v0 must be Lambda 
      if (TMath::Abs(v0.GetEffMass()-massLambda)>fMassWin) continue; 

      for (Int_t j=0; j<ntr; j++) {//loop on tracks
   Int_t bidx=trk[j];
   //Bo:   if (bidx==v->GetNindex()) continue; //bachelor and v0's negative tracks must be different
         if (bidx==v0.GetIndex(0)) continue; //Bo:  consistency 0 for neg
   AliESDtrack *btrk=event->GetTrack(bidx);
         if (btrk->GetSign()>0) continue;  // bachelor's charge 
          
       AliESDv0 *pv0=&v0;
         AliExternalTrackParam bt(*btrk), *pbt=&bt;

         Double_t dca=PropagateToDCA(pv0,pbt,b);
         if (dca > fDCAmax) continue;

         AliESDcascade cascade(*pv0,*pbt,bidx);//constucts a cascade candidate
   //PH        if (cascade.GetChi2Xi() > fChi2max) continue;

   Double_t x,y,z; cascade.GetXYZcascade(x,y,z); // Bo: bug correction
         Double_t r2=x*x + y*y; 
         if (r2 > fRmax2) continue;   // condition on fiducial zone
         if (r2 < fRmin2) continue;

   Double_t pxV0,pyV0,pzV0;
   pv0->GetPxPyPz(pxV0,pyV0,pzV0);
   if (x*pxV0+y*pyV0+z*pzV0 < 0) continue; //causality

         Double_t x1,y1,z1; pv0->GetXYZ(x1,y1,z1);
         if (r2 > (x1*x1+y1*y1)) continue;

     if (cascade.GetCascadeCosineOfPointingAngle(xPrimaryVertex,yPrimaryVertex,zPrimaryVertex) <fCPAmin) continue; //condition on the cascade pointing angle 
   
         cascade.SetDcaXiDaughters(dca);
   event->AddCascade(&cascade);
   v->SetUsedByCascade(kTRUE);
         ncasc++;
      } // end loop tracks
   } // end loop V0s

   // Looking for the anti-cascades...

   for (i=0; i<nV0; i++) { //loop on V0s
      AliESDv0 *v=(AliESDv0*)vtcs.UncheckedAt(i);
      AliESDv0 v0(*v);
      v0.ChangeMassHypothesis(kLambda0Bar); //the v0 must be anti-Lambda 
      if (TMath::Abs(v0.GetEffMass()-massLambda)>fMassWin) continue; 

      for (Int_t j=0; j<ntr; j++) {//loop on tracks
   Int_t bidx=trk[j];
   //Bo:   if (bidx==v->GetPindex()) continue; //bachelor and v0's positive tracks must be different
         if (bidx==v0.GetIndex(1)) continue; //Bo:  consistency 1 for pos
   AliESDtrack *btrk=event->GetTrack(bidx);
         if (btrk->GetSign()<0) continue;  // bachelor's charge 
          
   AliESDv0 *pv0=&v0;
         AliExternalTrackParam bt(*btrk), *pbt=&bt;

         Double_t dca=PropagateToDCA(pv0,pbt,b);
         if (dca > fDCAmax) continue;

         AliESDcascade cascade(*pv0,*pbt,bidx); //constucts a cascade candidate
   //PH         if (cascade.GetChi2Xi() > fChi2max) continue;

   Double_t x,y,z; cascade.GetXYZcascade(x,y,z); // Bo: bug correction
         Double_t r2=x*x + y*y; 
         if (r2 > fRmax2) continue;   // condition on fiducial zone
         if (r2 < fRmin2) continue;

   Double_t pxV0,pyV0,pzV0;
   pv0->GetPxPyPz(pxV0,pyV0,pzV0);
   if (x*pxV0+y*pyV0+z*pzV0 < 0) continue; //causality

         Double_t x1,y1,z1; pv0->GetXYZ(x1,y1,z1);
         if (r2 > (x1*x1+y1*y1)) continue;

   if (cascade.GetCascadeCosineOfPointingAngle(xPrimaryVertex,yPrimaryVertex,zPrimaryVertex) < fCPAmin) continue; //condition on the cascade pointing angle 

         cascade.SetDcaXiDaughters(dca);
   event->AddCascade(&cascade);
         ncasc++;

      } // end loop tracks
   } // end loop V0s

Info("V0sTracks2CascadeVertices","Number of reconstructed cascades: %d",ncasc);

   return 0;
}


Double_t AliCascadeVertexer::Det(Double_t a00, Double_t a01, Double_t a10, Double_t a11) const {
  //--------------------------------------------------------------------
  // This function calculates locally a 2x2 determinant
  //--------------------------------------------------------------------
  return a00*a11 - a01*a10;
}

Double_t AliCascadeVertexer::Det(Double_t a00,Double_t a01,Double_t a02,
         Double_t a10,Double_t a11,Double_t a12,
         Double_t a20,Double_t a21,Double_t a22) const {
  //--------------------------------------------------------------------
  // This function calculates locally a 3x3 determinant
  //--------------------------------------------------------------------
  return  a00*Det(a11,a12,a21,a22)-a01*Det(a10,a12,a20,a22)+a02*Det(a10,a11,a20,a21);
}




Double_t AliCascadeVertexer::PropagateToDCA(AliESDv0 *v, AliExternalTrackParam *t, Double_t b) {
  //--------------------------------------------------------------------
  // This function returns the DCA between the V0 and the track
  //--------------------------------------------------------------------
  Double_t alpha=t->GetAlpha(), cs1=TMath::Cos(alpha), sn1=TMath::Sin(alpha);
  Double_t r[3]; t->GetXYZ(r);
  Double_t x1=r[0], y1=r[1], z1=r[2];
  Double_t p[3]; t->GetPxPyPz(p);
  Double_t px1=p[0], py1=p[1], pz1=p[2];
  
  Double_t x2,y2,z2;     // position and momentum of V0
  Double_t px2,py2,pz2;
  
  v->GetXYZ(x2,y2,z2);
  v->GetPxPyPz(px2,py2,pz2);
 
// calculation dca
   
  Double_t dd= Det(x2-x1,y2-y1,z2-z1,px1,py1,pz1,px2,py2,pz2);
  Double_t ax= Det(py1,pz1,py2,pz2);
  Double_t ay=-Det(px1,pz1,px2,pz2);
  Double_t az= Det(px1,py1,px2,py2);

  Double_t dca=TMath::Abs(dd)/TMath::Sqrt(ax*ax + ay*ay + az*az);
  if (dca > fDCAmax) return 1.e+33;

//points of the DCA
  Double_t t1 = Det(x2-x1,y2-y1,z2-z1,px2,py2,pz2,ax,ay,az)/
                Det(px1,py1,pz1,px2,py2,pz2,ax,ay,az);
  
  x1 += px1*t1; y1 += py1*t1; //z1 += pz1*t1;
  
  if (x1*x1+y1*y1 > fRmaxMargin2) return 1.e+33;

  //propagate track to the points of DCA

  x1=x1*cs1 + y1*sn1;

  if (!t->PropagateTo(x1,b)) {
    AliError("Propagation failed");
    //    AliErrorF("Propagation failed for X=%f | V0: %f %f %f",x1,x2,y2,z2);
    //    t->Print();
    //
    return 1.e+33;
  }  

  return dca;
}