Adding new file also for the new Makefile
[u/mrichter/AliRoot.git] / ITS / AliV0vertex.cxx
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7f6ddf58 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 V0 vertex class
18//
19// Origin: Iouri Belikov, IReS, Strasbourg, Jouri.Belikov@cern.ch
20//-------------------------------------------------------------------------
21#include <iostream.h>
22#include <TMath.h>
23
24#include "AliV0vertex.h"
25#include "AliITStrackV2.h"
26
27ClassImp(AliV0vertex)
28
29AliV0vertex::AliV0vertex() : TObject() {
30 //--------------------------------------------------------------------
31 // Default constructor (K0s)
32 //--------------------------------------------------------------------
33 fPdgCode=kK0Short;
34 fEffMass=0.497672;
35 fChi2=1.e+33;
36 fPos[0]=fPos[1]=fPos[2]=0.;
37 fPosCov[0]=fPosCov[1]=fPosCov[2]=fPosCov[3]=fPosCov[4]=fPosCov[5]=0.;
38}
39
40AliV0vertex::AliV0vertex(const AliITStrackV2 &n, const AliITStrackV2 &p) {
41 //--------------------------------------------------------------------
42 // Main constructor
43 //--------------------------------------------------------------------
44 fPdgCode=kK0Short;
45 fNlab=n.GetLabel(); fPlab=p.GetLabel();
46
47 //Trivial estimation of the vertex parameters
48 Double_t pt, phi, x, par[5];
49 Double_t alpha, cs, sn;
50
51 n.GetExternalParameters(x,par); alpha=n.GetAlpha();
52 pt=1./TMath::Abs(par[4]);
53 phi=TMath::ASin(par[2]) + alpha;
54 Double_t px1=pt*TMath::Cos(phi), py1=pt*TMath::Sin(phi), pz1=pt*par[3];
55 cs=TMath::Cos(alpha); sn=TMath::Sin(alpha);
56 Double_t x1=x*cs - par[0]*sn;
57 Double_t y1=x*sn + par[0]*cs;
58 Double_t z1=par[1];
59 Double_t sx1=sn*sn*n.GetSigmaY2(), sy1=cs*cs*n.GetSigmaY2();
60
61 p.GetExternalParameters(x,par); alpha=p.GetAlpha();
62 pt=1./TMath::Abs(par[4]);
63 phi=TMath::ASin(par[2]) + alpha;
64 Double_t px2=pt*TMath::Cos(phi), py2=pt*TMath::Sin(phi), pz2=pt*par[3];
65 cs=TMath::Cos(alpha); sn=TMath::Sin(alpha);
66 Double_t x2=x*cs - par[0]*sn;
67 Double_t y2=x*sn + par[0]*cs;
68 Double_t z2=par[1];
69 Double_t sx2=sn*sn*p.GetSigmaY2(), sy2=cs*cs*p.GetSigmaY2();
70
71 Double_t sz1=n.GetSigmaZ2(), sz2=p.GetSigmaZ2();
72 Double_t wx1=sx2/(sx1+sx2), wx2=1.- wx1;
73 Double_t wy1=sy2/(sy1+sy2), wy2=1.- wy1;
74 Double_t wz1=sz2/(sz1+sz2), wz2=1.- wz1;
75 fPos[0]=wx1*x1 + wx2*x2; fPos[1]=wy1*y1 + wy2*y2; fPos[2]=wz1*z1 + wz2*z2;
76
77 //fPos[0]=0.5*(x1+x2); fPos[1]=0.5*(y1+y2); fPos[2]=0.5*(z1+z2);
78 fNmom[0]=px1; fNmom[1]=py1; fNmom[2]=pz1;
79 fPmom[0]=px2; fPmom[1]=py2; fPmom[2]=pz2;
80
81 Double_t e1=TMath::Sqrt(0.13957*0.13957 + px1*px1 + py1*py1 + pz1*pz1);
82 Double_t e2=TMath::Sqrt(0.13957*0.13957 + px2*px2 + py2*py2 + pz2*pz2);
83 fEffMass=TMath::Sqrt((e1+e2)*(e1+e2)-
84 (px1+px2)*(px1+px2)-(py1+py2)*(py1+py2)-(pz1+pz2)*(pz1+pz2));
85
86 fChi2=7.;
87}
88
89void AliV0vertex::ChangeMassHypothesis(Int_t code) {
90 //--------------------------------------------------------------------
91 // This function changes the mass hypothesis for this V0
92 //--------------------------------------------------------------------
93 Double_t nmass, pmass;
94
95 switch (code) {
96 case kLambda0:
97 nmass=0.13957; pmass=0.93827; break;
98 case kLambda0Bar:
99 pmass=0.13957; nmass=0.93827; break;
100 case kK0Short:
101 nmass=0.13957; pmass=0.13957; break;
102 default:
103 cerr<<"AliV0vertex::ChangeMassHypothesis: ";
104 cerr<<"invalide PDG code ! Assuming K0s...\n";
105 nmass=0.13957; pmass=0.13957; break;
106 }
107
108 Double_t px1=fNmom[0], py1=fNmom[1], pz1=fNmom[2];
109 Double_t px2=fPmom[0], py2=fPmom[1], pz2=fPmom[2];
110
111 Double_t e1=TMath::Sqrt(nmass*nmass + px1*px1 + py1*py1 + pz1*pz1);
112 Double_t e2=TMath::Sqrt(pmass*pmass + px2*px2 + py2*py2 + pz2*pz2);
113 fEffMass=TMath::Sqrt((e1+e2)*(e1+e2)-
114 (px1+px2)*(px1+px2)-(py1+py2)*(py1+py2)-(pz1+pz2)*(pz1+pz2));
115
116 fPdgCode=code;
117}
118
119void AliV0vertex::GetPxPyPz(Double_t &px, Double_t &py, Double_t &pz) const {
120 //--------------------------------------------------------------------
121 // This function returns V0's momentum (global)
122 //--------------------------------------------------------------------
123 px=fNmom[0]+fPmom[0];
124 py=fNmom[1]+fPmom[1];
125 pz=fNmom[2]+fPmom[2];
126}
127
128void AliV0vertex::GetXYZ(Double_t &x, Double_t &y, Double_t &z) const {
129 //--------------------------------------------------------------------
130 // This function returns V0's position (global)
131 //--------------------------------------------------------------------
132 x=fPos[0];
133 y=fPos[1];
134 z=fPos[2];
135}
136
137Double_t AliV0vertex::GetD(Double_t x0, Double_t y0, Double_t z0) const {
138 //--------------------------------------------------------------------
139 // This function returns V0's impact parameter
140 //--------------------------------------------------------------------
141 Double_t x=fPos[0],y=fPos[1],z=fPos[2];
142 Double_t px=fNmom[0]+fPmom[0];
143 Double_t py=fNmom[1]+fPmom[1];
144 Double_t pz=fNmom[2]+fPmom[2];
145
146 Double_t dx=(y0-y)*pz - (z0-z)*py;
147 Double_t dy=(x0-x)*pz - (z0-z)*px;
148 Double_t dz=(x0-x)*py - (y0-y)*px;
149 Double_t d=TMath::Sqrt((dx*dx+dy*dy+dz*dz)/(px*px+py*py+pz*pz));
150 return d;
151}