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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 | //------------------------------------------------------------------------- |
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21 | #include <Riostream.h> |
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22 | #include <TMath.h> |
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23 | #include <TPDGCode.h> |
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24 | |
| 25 | #include "AliV0vertex.h" |
| 26 | #include "AliITStrackV2.h" |
| 27 | |
| 28 | ClassImp(AliV0vertex) |
| 29 | |
| 30 | AliV0vertex::AliV0vertex() : TObject() { |
| 31 | //-------------------------------------------------------------------- |
| 32 | // Default constructor (K0s) |
| 33 | //-------------------------------------------------------------------- |
| 34 | fPdgCode=kK0Short; |
| 35 | fEffMass=0.497672; |
| 36 | fChi2=1.e+33; |
| 37 | fPos[0]=fPos[1]=fPos[2]=0.; |
| 38 | fPosCov[0]=fPosCov[1]=fPosCov[2]=fPosCov[3]=fPosCov[4]=fPosCov[5]=0.; |
| 39 | } |
| 40 | |
| 41 | AliV0vertex::AliV0vertex(const AliITStrackV2 &n, const AliITStrackV2 &p) { |
| 42 | //-------------------------------------------------------------------- |
| 43 | // Main constructor |
| 44 | //-------------------------------------------------------------------- |
| 45 | fPdgCode=kK0Short; |
| 46 | fNlab=n.GetLabel(); fPlab=p.GetLabel(); |
| 47 | |
| 48 | //Trivial estimation of the vertex parameters |
| 49 | Double_t pt, phi, x, par[5]; |
| 50 | Double_t alpha, cs, sn; |
| 51 | |
| 52 | n.GetExternalParameters(x,par); alpha=n.GetAlpha(); |
| 53 | pt=1./TMath::Abs(par[4]); |
| 54 | phi=TMath::ASin(par[2]) + alpha; |
| 55 | Double_t px1=pt*TMath::Cos(phi), py1=pt*TMath::Sin(phi), pz1=pt*par[3]; |
| 56 | cs=TMath::Cos(alpha); sn=TMath::Sin(alpha); |
| 57 | Double_t x1=x*cs - par[0]*sn; |
| 58 | Double_t y1=x*sn + par[0]*cs; |
| 59 | Double_t z1=par[1]; |
| 60 | Double_t sx1=sn*sn*n.GetSigmaY2(), sy1=cs*cs*n.GetSigmaY2(); |
| 61 | |
| 62 | p.GetExternalParameters(x,par); alpha=p.GetAlpha(); |
| 63 | pt=1./TMath::Abs(par[4]); |
| 64 | phi=TMath::ASin(par[2]) + alpha; |
| 65 | Double_t px2=pt*TMath::Cos(phi), py2=pt*TMath::Sin(phi), pz2=pt*par[3]; |
| 66 | cs=TMath::Cos(alpha); sn=TMath::Sin(alpha); |
| 67 | Double_t x2=x*cs - par[0]*sn; |
| 68 | Double_t y2=x*sn + par[0]*cs; |
| 69 | Double_t z2=par[1]; |
| 70 | Double_t sx2=sn*sn*p.GetSigmaY2(), sy2=cs*cs*p.GetSigmaY2(); |
| 71 | |
| 72 | Double_t sz1=n.GetSigmaZ2(), sz2=p.GetSigmaZ2(); |
| 73 | Double_t wx1=sx2/(sx1+sx2), wx2=1.- wx1; |
| 74 | Double_t wy1=sy2/(sy1+sy2), wy2=1.- wy1; |
| 75 | Double_t wz1=sz2/(sz1+sz2), wz2=1.- wz1; |
| 76 | fPos[0]=wx1*x1 + wx2*x2; fPos[1]=wy1*y1 + wy2*y2; fPos[2]=wz1*z1 + wz2*z2; |
| 77 | |
| 78 | //fPos[0]=0.5*(x1+x2); fPos[1]=0.5*(y1+y2); fPos[2]=0.5*(z1+z2); |
| 79 | fNmom[0]=px1; fNmom[1]=py1; fNmom[2]=pz1; |
| 80 | fPmom[0]=px2; fPmom[1]=py2; fPmom[2]=pz2; |
| 81 | |
| 82 | Double_t e1=TMath::Sqrt(0.13957*0.13957 + px1*px1 + py1*py1 + pz1*pz1); |
| 83 | Double_t e2=TMath::Sqrt(0.13957*0.13957 + px2*px2 + py2*py2 + pz2*pz2); |
| 84 | fEffMass=TMath::Sqrt((e1+e2)*(e1+e2)- |
| 85 | (px1+px2)*(px1+px2)-(py1+py2)*(py1+py2)-(pz1+pz2)*(pz1+pz2)); |
| 86 | |
| 87 | fChi2=7.; |
| 88 | } |
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89 | /* |
| 90 | Double_t AliV0vertex::ChangeMassHypothesis(Int_t code) { |
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91 | //-------------------------------------------------------------------- |
| 92 | // This function changes the mass hypothesis for this V0 |
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93 | // and returns the "kinematical quality" of this hypothesis |
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94 | //-------------------------------------------------------------------- |
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95 | Double_t nmass=0.13957, pmass=0.13957, mass=0.49767, des=0; |
| 96 | |
| 97 | fPdgCode=code; |
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98 | |
| 99 | switch (code) { |
| 100 | case kLambda0: |
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101 | nmass=0.13957; pmass=0.93827; mass=1.1157; des=0.9437-0.1723; break; |
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102 | case kLambda0Bar: |
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103 | pmass=0.13957; nmass=0.93827; mass=1.1157; des=0.1723-0.9437; break; |
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104 | case kK0Short: |
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105 | break; |
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106 | default: |
| 107 | cerr<<"AliV0vertex::ChangeMassHypothesis: "; |
| 108 | cerr<<"invalide PDG code ! Assuming K0s...\n"; |
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109 | fPdgCode=kK0Short; |
| 110 | break; |
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111 | } |
| 112 | |
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113 | Double_t pxn=fNmom[0], pyn=fNmom[1], pzn=fNmom[2]; |
| 114 | Double_t pxp=fPmom[0], pyp=fPmom[1], pzp=fPmom[2]; |
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115 | |
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116 | Double_t en=TMath::Sqrt(nmass*nmass + pxn*pxn + pyn*pyn + pzn*pzn); |
| 117 | Double_t ep=TMath::Sqrt(pmass*pmass + pxp*pxp + pyp*pyp + pzp*pzp); |
| 118 | Double_t pxl=pxn+pxp, pyl=pyn+pyp, pzl=pzn+pzp; |
| 119 | Double_t pl=TMath::Sqrt(pxl*pxl + pyl*pyl + pzl*pzl); |
| 120 | |
| 121 | fEffMass=TMath::Sqrt((en+ep)*(en+ep)-pl*pl); |
| 122 | |
| 123 | Double_t gamma=(en+ep)/mass, betagamma=pl/mass; |
| 124 | Double_t pln=(pxn*pxl + pyn*pyl + pzn*pzl)/pl; |
| 125 | Double_t plp=(pxp*pxl + pyp*pyl + pzp*pzl)/pl; |
| 126 | Double_t plps=gamma*plp - betagamma*ep; |
| 127 | |
| 128 | Double_t diff=2*gamma*plps + betagamma*des; |
| 129 | |
| 130 | return (plp-pln-diff); |
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131 | |
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132 | } |
| 133 | */ |
| 134 | Double_t AliV0vertex::ChangeMassHypothesis(Int_t code) { |
| 135 | //-------------------------------------------------------------------- |
| 136 | // This function changes the mass hypothesis for this V0 |
| 137 | // and returns the "kinematical quality" of this hypothesis |
| 138 | //-------------------------------------------------------------------- |
| 139 | Double_t nmass=0.13957, pmass=0.13957, mass=0.49767, ps=0.206; |
| 140 | |
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141 | fPdgCode=code; |
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142 | |
| 143 | switch (code) { |
| 144 | case kLambda0: |
| 145 | nmass=0.13957; pmass=0.93827; mass=1.1157; ps=0.101; break; |
| 146 | case kLambda0Bar: |
| 147 | pmass=0.13957; nmass=0.93827; mass=1.1157; ps=0.101; break; |
| 148 | case kK0Short: |
| 149 | break; |
| 150 | default: |
| 151 | cerr<<"AliV0vertex::ChangeMassHypothesis: "; |
| 152 | cerr<<"invalide PDG code ! Assuming K0s...\n"; |
| 153 | fPdgCode=kK0Short; |
| 154 | break; |
| 155 | } |
| 156 | |
| 157 | Double_t pxn=fNmom[0], pyn=fNmom[1], pzn=fNmom[2]; |
| 158 | Double_t pxp=fPmom[0], pyp=fPmom[1], pzp=fPmom[2]; |
| 159 | |
| 160 | Double_t en=TMath::Sqrt(nmass*nmass + pxn*pxn + pyn*pyn + pzn*pzn); |
| 161 | Double_t ep=TMath::Sqrt(pmass*pmass + pxp*pxp + pyp*pyp + pzp*pzp); |
| 162 | Double_t pxl=pxn+pxp, pyl=pyn+pyp, pzl=pzn+pzp; |
| 163 | Double_t pl=TMath::Sqrt(pxl*pxl + pyl*pyl + pzl*pzl); |
| 164 | |
| 165 | fEffMass=TMath::Sqrt((en+ep)*(en+ep)-pl*pl); |
| 166 | |
| 167 | Double_t beta=pl/(en+ep); |
| 168 | Double_t pln=(pxn*pxl + pyn*pyl + pzn*pzl)/pl; |
| 169 | Double_t plp=(pxp*pxl + pyp*pyl + pzp*pzl)/pl; |
| 170 | |
| 171 | Double_t pt2=pxp*pxp + pyp*pyp + pzp*pzp - plp*plp; |
| 172 | |
| 173 | Double_t a=(plp-pln)/(plp+pln); |
| 174 | a -= (pmass*pmass-nmass*nmass)/(mass*mass); |
| 175 | a = 0.25*beta*beta*mass*mass*a*a + pt2; |
| 176 | |
| 177 | return (a - ps*ps); |
| 178 | |
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179 | } |
| 180 | |
| 181 | void AliV0vertex::GetPxPyPz(Double_t &px, Double_t &py, Double_t &pz) const { |
| 182 | //-------------------------------------------------------------------- |
| 183 | // This function returns V0's momentum (global) |
| 184 | //-------------------------------------------------------------------- |
| 185 | px=fNmom[0]+fPmom[0]; |
| 186 | py=fNmom[1]+fPmom[1]; |
| 187 | pz=fNmom[2]+fPmom[2]; |
| 188 | } |
| 189 | |
| 190 | void AliV0vertex::GetXYZ(Double_t &x, Double_t &y, Double_t &z) const { |
| 191 | //-------------------------------------------------------------------- |
| 192 | // This function returns V0's position (global) |
| 193 | //-------------------------------------------------------------------- |
| 194 | x=fPos[0]; |
| 195 | y=fPos[1]; |
| 196 | z=fPos[2]; |
| 197 | } |
| 198 | |
| 199 | Double_t AliV0vertex::GetD(Double_t x0, Double_t y0, Double_t z0) const { |
| 200 | //-------------------------------------------------------------------- |
| 201 | // This function returns V0's impact parameter |
| 202 | //-------------------------------------------------------------------- |
| 203 | Double_t x=fPos[0],y=fPos[1],z=fPos[2]; |
| 204 | Double_t px=fNmom[0]+fPmom[0]; |
| 205 | Double_t py=fNmom[1]+fPmom[1]; |
| 206 | Double_t pz=fNmom[2]+fPmom[2]; |
| 207 | |
| 208 | Double_t dx=(y0-y)*pz - (z0-z)*py; |
| 209 | Double_t dy=(x0-x)*pz - (z0-z)*px; |
| 210 | Double_t dz=(x0-x)*py - (y0-y)*px; |
| 211 | Double_t d=TMath::Sqrt((dx*dx+dy*dy+dz*dz)/(px*px+py*py+pz*pz)); |
| 212 | return d; |
| 213 | } |
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