+/**************************************************************************
+ * 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. *
+ **************************************************************************/
+
+//-------------------------------------------------------------------------
+// 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 "AliLightCascadeVertexer.h"
+
+ClassImp(AliLightCascadeVertexer)
+
+//A set of loose cuts
+Double_t
+ AliLightCascadeVertexer::fgChi2max=33.; //maximal allowed chi2
+Double_t
+ AliLightCascadeVertexer::fgDV0min=0.01; //min V0 impact parameter
+Double_t
+ AliLightCascadeVertexer::fgMassWin=0.008; //"window" around the Lambda mass
+Double_t
+ AliLightCascadeVertexer::fgDBachMin=0.01; //min bachelor impact parameter
+Double_t
+ AliLightCascadeVertexer::fgDCAmax=2.0; //max DCA between the V0 and the track
+Double_t
+ AliLightCascadeVertexer::fgCPAmin=0.98; //min cosine of the cascade pointing angle
+Double_t
+ AliLightCascadeVertexer::fgRmin=0.2; //min radius of the fiducial volume
+Double_t
+ AliLightCascadeVertexer::fgRmax=100.; //max radius of the fiducial volume
+
+Double_t AliLightCascadeVertexer::fgMaxEta=0.8; //max |eta|
+Double_t AliLightCascadeVertexer::fgMinClusters=70; //min clusters (>=)
+
+
+Int_t AliLightCascadeVertexer::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();
+ TArrayI trk(nentr); Int_t ntr=0;
+ for (i=0; i<nentr; i++) {
+ AliESDtrack *esdtr=event->GetTrack(i);
+ ULong_t status=esdtr->GetStatus();
+
+ if ((status&AliESDtrack::kITSrefit)==0)
+ if ((status&AliESDtrack::kTPCrefit)==0) continue;
+
+ //Track pre-selection: clusters
+ if (esdtr->GetTPCNcls() < fMinClusters ) 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;
+
+ //eta cut - test
+ if (TMath::Abs(pbt->Eta())>fMaxEta) 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 > fRmax*fRmax) continue; // condition on fiducial zone
+ if (r2 < fRmin*fRmin) 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
+
+ // 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 > fRmax*fRmax) continue; // condition on fiducial zone
+ if (r2 < fRmin*fRmin) 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 AliLightCascadeVertexer::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 AliLightCascadeVertexer::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 AliLightCascadeVertexer::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);
+
+//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;
+
+
+ //propagate track to the points of DCA
+
+ x1=x1*cs1 + y1*sn1;
+ if (!t->PropagateTo(x1,b)) {
+ Error("PropagateToDCA","Propagation failed !");
+ return 1.e+33;
+ }
+
+ return dca;
+}
+
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