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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 | ||
27 | ClassImp(AliV0vertex) | |
28 | ||
29 | AliV0vertex::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 | ||
40 | AliV0vertex::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 | ||
89 | void 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 | ||
119 | void 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 | ||
128 | void 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 | ||
137 | Double_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 | } |