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[u/mrichter/AliRoot.git] / ITS / AliCascadeVertex.cxx
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a9a2d814 1/**************************************************************************
2 * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
3 * *
4 * Author: The ALICE Off-line Project. *
5 * Contributors are mentioned in the code where appropriate. *
6 * *
7 * Permission to use, copy, modify and distribute this software and its *
8 * documentation strictly for non-commercial purposes is hereby granted *
9 * without fee, provided that the above copyright notice appears in all *
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 **************************************************************************/
15
16//-------------------------------------------------------------------------
17// Implementation of the cascade vertex class
18//
19// Origin: Christian Kuhn, IReS, Strasbourg, christian.kuhn@ires.in2p3.fr
20//-------------------------------------------------------------------------
a9a2d814 21#include <TMath.h>
22
23#include "AliCascadeVertex.h"
a9a2d814 24#include "AliITStrackV2.h"
116cbefd 25#include "AliV0vertex.h"
a9a2d814 26
27ClassImp(AliCascadeVertex)
28
a9a2d814 29
30inline Double_t det(Double_t a00, Double_t a01, Double_t a10, Double_t a11){
31 // determinant 2x2
32 return a00*a11 - a01*a10;
33}
34
35inline 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) {
38 // determinant 3x3
39 return
40 a00*det(a11,a12,a21,a22)-a01*det(a10,a12,a20,a22)+a02*det(a10,a11,a20,a21);
41}
42
43
a9a2d814 44AliCascadeVertex::AliCascadeVertex(const AliV0vertex &v,const AliITStrackV2 &t) {
45 //--------------------------------------------------------------------
46 // Main constructor
47 //--------------------------------------------------------------------
48 fPdgCode=kXiMinus;
49
e23730c7 50 fV0idx[0]=v.GetNindex(); fV0idx[1]=v.GetPindex();
51 fBachIdx=t.GetLabel();
a9a2d814 52
53 //Trivial estimation of the vertex parameters
54 Double_t pt, phi, x, par[5];
55 Double_t alpha, cs, sn;
56
57 t.GetExternalParameters(x,par); alpha=t.GetAlpha();
58 pt=1./TMath::Abs(par[4]);
59 phi=TMath::ASin(par[2]) + alpha;
60
61 // momentum of the bachelor track
62
63 Double_t px1=pt*TMath::Cos(phi), py1=pt*TMath::Sin(phi), pz1=pt*par[3];
64
65 cs=TMath::Cos(alpha); sn=TMath::Sin(alpha);
66
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;
69 Double_t z1=par[1];
70
71 Double_t x2,y2,z2; // position of the V0
72 v.GetXYZ(x2,y2,z2);
73
74 Double_t px2,py2,pz2; // momentum of V0
75 v.GetPxPyPz(px2,py2,pz2);
76
77 Double_t a2=((x1-x2)*px2+(y1-y2)*py2+(z1-z2)*pz2)/(px2*px2+py2*py2+pz2*pz2);
78
79 Double_t xm=x2+a2*px2;
80 Double_t ym=y2+a2*py2;
81 Double_t zm=z2+a2*pz2;
82
83 // position of the cascade decay
84
85 fPos[0]=0.5*(x1+xm); fPos[1]=0.5*(y1+ym); fPos[2]=0.5*(z1+zm);
04b2a5f1 86
87
a9a2d814 88 // invariant mass of the cascade (default is Ximinus)
89
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);
92
93 fEffMass=TMath::Sqrt((e1+e2)*(e1+e2)-
94 (px1+px2)*(px1+px2)-(py1+py2)*(py1+py2)-(pz1+pz2)*(pz1+pz2));
95
04b2a5f1 96
97 // momenta of the bachelor and the V0
98
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;
104
105
a9a2d814 106 fChi2=7.;
107
108}
109
04b2a5f1 110