1 /**************************************************************************
2 * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
4 * Author: The ALICE Off-line Project. *
5 * Contributors are mentioned in the code where appropriate. *
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8 * documentation strictly for non-commercial purposes is hereby granted *
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10 * copies and that both the copyright notice and this permission notice *
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 **************************************************************************/
16 //-------------------------------------------------------------------------
17 // Implementation of the cascade vertexer class
19 // Origin: Christian Kuhn, IReS, Strasbourg, christian.kuhn@ires.in2p3.fr
20 //-------------------------------------------------------------------------
21 #include <Riostream.h>
22 #include <TObjArray.h>
26 #include "AliCascadeVertex.h"
27 #include "AliCascadeVertexer.h"
28 #include "AliITStrackV2.h"
29 #include "AliV0vertex.h"
31 ClassImp(AliCascadeVertexer)
33 Int_t AliCascadeVertexer::
34 V0sTracks2CascadeVertices(TTree *vTree,TTree *tTree, TTree *xTree) {
35 //--------------------------------------------------------------------
36 // This function reconstructs cascade vertices
37 //--------------------------------------------------------------------
38 TBranch *branch=vTree->GetBranch("vertices");
40 Error("V0sTracks2CascadeVertices","Can't get the V0 branch !");
43 Int_t nentrV0=(Int_t)vTree->GetEntries();
45 TObjArray vtxV0(nentrV0);
47 // fill TObjArray vtxV0 with vertices
50 for (i=0; i<nentrV0; i++) {
52 AliV0vertex *ioVertex=new AliV0vertex;
53 branch->SetAddress(&ioVertex);
56 vtxV0.AddLast(ioVertex);
60 branch=tTree->GetBranch("tracks");
62 Error("V0sTracks2CascadeVertices","Can't get the track branch !");
65 Int_t nentr=(Int_t)tTree->GetEntries();
67 TObjArray trks(nentr);
69 // fill TObjArray trks with tracks
73 for (i=0; i<nentr; i++) {
75 AliITStrackV2 *iotrack=new AliITStrackV2;
76 branch->SetAddress(&iotrack);
79 iotrack->PropagateTo(3.,0.0023,65.19); iotrack->PropagateTo(2.5,0.,0.);
81 ntrack++; trks.AddLast(iotrack);
85 AliCascadeVertex *ioCascade=0;
86 branch=xTree->GetBranch("cascades");
87 if (!branch) xTree->Branch("cascades","AliCascadeVertex",&ioCascade,32000,3);
88 else branch->SetAddress(&ioCascade);
90 // loop on all vertices
92 Double_t massLambda=1.11568;
95 for (i=0; i<nV0; i++) {
97 AliV0vertex *V0ver=(AliV0vertex *)vtxV0.UncheckedAt(i);
99 V0ver->ChangeMassHypothesis(kLambda0); //I.B.
101 if (V0ver->GetEffMass()<massLambda-fMassWin || // condition of the V0 mass window (cut fMassWin)
102 V0ver->GetEffMass()>massLambda+fMassWin) continue;
104 if (V0ver->GetD(0,0,0)<fDV0min) continue; // condition of minimum impact parameter of the V0 (cut fDV0min)
105 // here why not cuting on pointing angle ???
107 // for each vertex in the good mass range, loop on all tracks (= bachelor candidates)
109 for (Int_t k=0; k<ntrack; k++) {
111 AliITStrackV2 *bachtrk=(AliITStrackV2 *)trks.UncheckedAt(k);
113 if (TMath::Abs(bachtrk->GetD())<fDBachMin) continue; // eliminate to small impact parameters
115 if (V0ver->GetPdgCode()==kLambda0 && bachtrk->Get1Pt()<0.) continue; // condition on V0 label
116 if (V0ver->GetPdgCode()==kLambda0Bar && bachtrk->Get1Pt()>0.) continue; // + good sign for bachelor
118 AliV0vertex V0(*V0ver), *pV0=&V0;
119 AliITStrackV2 bt(*bachtrk), *pbt=&bt;
121 // calculation of the distance of closest approach between the V0 and the bachelor
123 Double_t dca=PropagateToDCA(pV0,pbt);
124 if (dca > fDCAmax) continue; // cut on dca
126 // construction of a cascade object
128 AliCascadeVertex cascade(*pV0,*pbt);
129 if (cascade.GetChi2() > fChi2max) continue;
131 // get cascade decay position (V0, bachelor)
133 Double_t x,y,z; cascade.GetXYZ(x,y,z);
134 Double_t r2=x*x + y*y;
135 if (r2 > fRmax*fRmax) continue; // condition on fiducial zone
136 if (r2 < fRmin*fRmin) continue;
140 Double_t x1,y1,z1; V0ver->GetXYZ(x1,y1,z1);
141 if (r2 > (x1*x1+y1*y1)) continue;
142 if (z*z > z1*z1) continue;
145 // get cascade momentum
147 Double_t px,py,pz; cascade.GetPxPyPz(px,py,pz);
148 Double_t p2=px*px+py*py+pz*pz;
149 Double_t cost=(x*px+y*py+z*pz)/TMath::Sqrt(p2*(r2+z*z));
151 if (cost<fCPAmax) continue; // condition on the cascade pointing angle
153 //cascade.ChangeMassHypothesis(); //default is Xi
156 ioCascade=&cascade; xTree->Fill();
163 cerr<<"Number of reconstructed cascades: "<<ncasc<<endl;
171 inline Double_t det(Double_t a00, Double_t a01, Double_t a10, Double_t a11){
173 return a00*a11 - a01*a10;
176 inline Double_t det (Double_t a00,Double_t a01,Double_t a02,
177 Double_t a10,Double_t a11,Double_t a12,
178 Double_t a20,Double_t a21,Double_t a22) {
181 a00*det(a11,a12,a21,a22)-a01*det(a10,a12,a20,a22)+a02*det(a10,a11,a20,a21);
188 AliCascadeVertexer::PropagateToDCA(AliV0vertex *v, AliITStrackV2 *t) {
189 //--------------------------------------------------------------------
190 // This function returns the DCA between the V0 and the track
191 //--------------------------------------------------------------------
193 Double_t phi, x, par[5];
194 Double_t alpha, cs1, sn1;
196 t->GetExternalParameters(x,par); alpha=t->GetAlpha();
197 phi=TMath::ASin(par[2]) + alpha;
198 Double_t px1=TMath::Cos(phi), py1=TMath::Sin(phi), pz1=par[3];
201 cs1=TMath::Cos(alpha); sn1=TMath::Sin(alpha);
202 Double_t x1=x*cs1 - par[0]*sn1;
203 Double_t y1=x*sn1 + par[0]*cs1;
207 Double_t x2,y2,z2; // position and momentum of V0
208 Double_t px2,py2,pz2;
211 v->GetPxPyPz(px2,py2,pz2);
215 Double_t dd= det(x2-x1,y2-y1,z2-z1,px1,py1,pz1,px2,py2,pz2);
216 Double_t ax= det(py1,pz1,py2,pz2);
217 Double_t ay=-det(px1,pz1,px2,pz2);
218 Double_t az= det(px1,py1,px2,py2);
220 Double_t dca=TMath::Abs(dd)/TMath::Sqrt(ax*ax + ay*ay + az*az);
223 Double_t t1 = det(x2-x1,y2-y1,z2-z1,px2,py2,pz2,ax,ay,az)/
224 det(px1,py1,pz1,px2,py2,pz2,ax,ay,az);
226 x1 += px1*t1; y1 += py1*t1; //z1 += pz1*t1;
229 //propagate track to the points of DCA
232 if (!t->PropagateTo(x1,0.,0.)) {
233 cerr<<"AliV0vertexer::PropagateToDCA: propagation failed !\n";