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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11 * appear in the supporting documentation. The authors make no claims *
12 * about the suitability of this software for any purpose. It is *
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14 **************************************************************************/
16 //-------------------------------------------------------------------------
17 // Implementation of the cascade vertex class
19 // Origin: Christian Kuhn, IReS, Strasbourg, christian.kuhn@ires.in2p3.fr
20 //-------------------------------------------------------------------------
23 #include "AliCascadeVertex.h"
24 #include "AliITStrackV2.h"
25 #include "AliV0vertex.h"
27 ClassImp(AliCascadeVertex)
30 inline Double_t det(Double_t a00, Double_t a01, Double_t a10, Double_t a11){
32 return a00*a11 - a01*a10;
35 inline Double_t det (Double_t a00,Double_t a01,Double_t a02,
36 Double_t a10,Double_t a11,Double_t a12,
37 Double_t a20,Double_t a21,Double_t a22) {
40 a00*det(a11,a12,a21,a22)-a01*det(a10,a12,a20,a22)+a02*det(a10,a11,a20,a21);
44 AliCascadeVertex::AliCascadeVertex(const AliV0vertex &v,const AliITStrackV2 &t) {
45 //--------------------------------------------------------------------
47 //--------------------------------------------------------------------
50 fV0idx[0]=v.GetNindex(); fV0idx[1]=v.GetPindex();
51 fBachIdx=t.GetLabel();
53 //Trivial estimation of the vertex parameters
54 Double_t pt, phi, x, par[5];
55 Double_t alpha, cs, sn;
57 t.GetExternalParameters(x,par); alpha=t.GetAlpha();
58 pt=1./TMath::Abs(par[4]);
59 phi=TMath::ASin(par[2]) + alpha;
61 // momentum of the bachelor track
63 Double_t px1=pt*TMath::Cos(phi), py1=pt*TMath::Sin(phi), pz1=pt*par[3];
65 cs=TMath::Cos(alpha); sn=TMath::Sin(alpha);
67 Double_t x1=x*cs - par[0]*sn; // position of the bachelor at dca (bachelor,V0)
68 Double_t y1=x*sn + par[0]*cs;
71 Double_t x2,y2,z2; // position of the V0
74 Double_t px2,py2,pz2; // momentum of V0
75 v.GetPxPyPz(px2,py2,pz2);
77 Double_t a2=((x1-x2)*px2+(y1-y2)*py2+(z1-z2)*pz2)/(px2*px2+py2*py2+pz2*pz2);
79 Double_t xm=x2+a2*px2;
80 Double_t ym=y2+a2*py2;
81 Double_t zm=z2+a2*pz2;
83 // position of the cascade decay
85 fPos[0]=0.5*(x1+xm); fPos[1]=0.5*(y1+ym); fPos[2]=0.5*(z1+zm);
88 // invariant mass of the cascade (default is Ximinus)
90 Double_t e1=TMath::Sqrt(0.13957*0.13957 + px1*px1 + py1*py1 + pz1*pz1);
91 Double_t e2=TMath::Sqrt(1.11568*1.11568 + px2*px2 + py2*py2 + pz2*pz2);
93 fEffMass=TMath::Sqrt((e1+e2)*(e1+e2)-
94 (px1+px2)*(px1+px2)-(py1+py2)*(py1+py2)-(pz1+pz2)*(pz1+pz2));
97 // momenta of the bachelor and the V0
99 fBachMom[0]=px1; fBachMom[1]=py1; fBachMom[2]=pz1;
100 v.GetNPxPyPz(px2,py2,pz2);
101 fV0mom[0][0]=px2; fV0mom[0][1]=py2; fV0mom[0][2]=pz2;
102 v.GetPPxPyPz(px2,py2,pz2);
103 fV0mom[1][0]=px2; fV0mom[1][1]=py2; fV0mom[1][2]=pz2;