/************************************************************************** * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. * * * * Author: The ALICE Off-line Project. * * Contributors are mentioned in the code where appropriate. * * * * Permission to use, copy, modify and distribute this software and its * * documentation strictly for non-commercial purposes is hereby granted * * without fee, provided that the above copyright notice appears in all * * copies and that both the copyright notice and this permission notice * * appear in the supporting documentation. The authors make no claims * * about the suitability of this software for any purpose. It is * * provided "as is" without express or implied warranty. * **************************************************************************/ //------------------------------------------------------------------------- // Implementation of the cascade vertex class // // Origin: Christian Kuhn, IReS, Strasbourg, christian.kuhn@ires.in2p3.fr //------------------------------------------------------------------------- #include #include #include "AliCascadeVertex.h" #include "AliV0vertex.h" #include "AliITStrackV2.h" ClassImp(AliCascadeVertex) AliCascadeVertex::AliCascadeVertex() : TObject() { //-------------------------------------------------------------------- // Default constructor (Xi-) //-------------------------------------------------------------------- fPdgCode=kXiMinus; fEffMass=1.32131; fChi2=1.e+33; fPos[0]=fPos[1]=fPos[2]=0.; fPosCov[0]=fPosCov[1]=fPosCov[2]=fPosCov[3]=fPosCov[4]=fPosCov[5]=0.; } inline Double_t det(Double_t a00, Double_t a01, Double_t a10, Double_t a11){ // determinant 2x2 return a00*a11 - a01*a10; } inline Double_t det (Double_t a00,Double_t a01,Double_t a02, Double_t a10,Double_t a11,Double_t a12, Double_t a20,Double_t a21,Double_t a22) { // determinant 3x3 return a00*det(a11,a12,a21,a22)-a01*det(a10,a12,a20,a22)+a02*det(a10,a11,a20,a21); } AliCascadeVertex::AliCascadeVertex(const AliV0vertex &v,const AliITStrackV2 &t) { //-------------------------------------------------------------------- // Main constructor //-------------------------------------------------------------------- fPdgCode=kXiMinus; fV0lab[0]=v.GetNlabel(); fV0lab[1]=v.GetPlabel(); fBachLab=t.GetLabel(); //Trivial estimation of the vertex parameters Double_t pt, phi, x, par[5]; Double_t alpha, cs, sn; t.GetExternalParameters(x,par); alpha=t.GetAlpha(); pt=1./TMath::Abs(par[4]); phi=TMath::ASin(par[2]) + alpha; // momentum of the bachelor track Double_t px1=pt*TMath::Cos(phi), py1=pt*TMath::Sin(phi), pz1=pt*par[3]; cs=TMath::Cos(alpha); sn=TMath::Sin(alpha); Double_t x1=x*cs - par[0]*sn; // position of the bachelor at dca (bachelor,V0) Double_t y1=x*sn + par[0]*cs; Double_t z1=par[1]; Double_t x2,y2,z2; // position of the V0 v.GetXYZ(x2,y2,z2); Double_t px2,py2,pz2; // momentum of V0 v.GetPxPyPz(px2,py2,pz2); Double_t a2=((x1-x2)*px2+(y1-y2)*py2+(z1-z2)*pz2)/(px2*px2+py2*py2+pz2*pz2); Double_t xm=x2+a2*px2; Double_t ym=y2+a2*py2; Double_t zm=z2+a2*pz2; // position of the cascade decay fPos[0]=0.5*(x1+xm); fPos[1]=0.5*(y1+ym); fPos[2]=0.5*(z1+zm); // momenta of the bachelor and the V0 fBachMom[0]=px1; fBachMom[1]=py1; fBachMom[2]=pz1; fV0mom[0]=px2; fV0mom[1]=py2; fV0mom[2]=pz2; // invariant mass of the cascade (default is Ximinus) Double_t e1=TMath::Sqrt(0.13957*0.13957 + px1*px1 + py1*py1 + pz1*pz1); Double_t e2=TMath::Sqrt(1.11568*1.11568 + px2*px2 + py2*py2 + pz2*pz2); fEffMass=TMath::Sqrt((e1+e2)*(e1+e2)- (px1+px2)*(px1+px2)-(py1+py2)*(py1+py2)-(pz1+pz2)*(pz1+pz2)); fChi2=7.; } void AliCascadeVertex::ChangeMassHypothesis(Int_t code) { //-------------------------------------------------------------------- // This function changes the mass hypothesis for this cascade //-------------------------------------------------------------------- // HOW TO DISTINGUISH BETWEEN A XIMINUS AND A XIPLUS ?????????? // SAME QUESTION FOR (ANTI-)OMEGA'S (here) ... AND FOR (ANTI-)LAMBDAS (in AliV0vertex) ?? // -> NEED ADDITIONAL CONDITION ON BACHELOR AND V0 PDGCODE !!!! BUT in the ANALYSIS MACROS !!! Double_t massBach, massV0; switch (code) { case kXiMinus: massBach=0.13957; massV0=1.11568; break; case kXiPlusBar: massBach=0.13957; massV0=1.11568; break; case kOmegaMinus: massBach=0.49368; massV0=1.11568; break; case kOmegaPlusBar: massBach=0.49368; massV0=1.11568; break; default: cerr<<"AliCascadeVertex::ChangeMassHypothesis: "; cerr<<"invalide PDG code ! Assuming XiMinus's...\n"; massBach=0.13957; massV0=1.11568; break; } Double_t px1=fBachMom[0], py1=fBachMom[1], pz1=fBachMom[2]; Double_t px2=fV0mom[0], py2=fV0mom[1], pz2=fV0mom[2]; Double_t e1=TMath::Sqrt(massBach*massBach + px1*px1 + py1*py1 + pz1*pz1); Double_t e2=TMath::Sqrt(massV0*massV0 + px2*px2 + py2*py2 + pz2*pz2); fEffMass=TMath::Sqrt((e1+e2)*(e1+e2)- (px1+px2)*(px1+px2)-(py1+py2)*(py1+py2)-(pz1+pz2)*(pz1+pz2)); fPdgCode=code; } void AliCascadeVertex::GetPxPyPz(Double_t &px, Double_t &py, Double_t &pz) const { //-------------------------------------------------------------------- // This function returns the cascade momentum (global) //-------------------------------------------------------------------- px=fV0mom[0]+fBachMom[0]; py=fV0mom[1]+fBachMom[1]; pz=fV0mom[2]+fBachMom[2]; } void AliCascadeVertex::GetXYZ(Double_t &x, Double_t &y, Double_t &z) const { //-------------------------------------------------------------------- // This function returns cascade position (global) //-------------------------------------------------------------------- x=fPos[0]; y=fPos[1]; z=fPos[2]; } Double_t AliCascadeVertex::GetD(Double_t x0, Double_t y0, Double_t z0) const { //-------------------------------------------------------------------- // This function returns the cascade impact parameter //-------------------------------------------------------------------- Double_t x=fPos[0],y=fPos[1],z=fPos[2]; Double_t px=fV0mom[0]+fBachMom[0]; Double_t py=fV0mom[1]+fBachMom[1]; Double_t pz=fV0mom[2]+fBachMom[2]; Double_t dx=(y0-y)*pz - (z0-z)*py; Double_t dy=(x0-x)*pz - (z0-z)*px; Double_t dz=(x0-x)*py - (y0-y)*px; Double_t d=TMath::Sqrt((dx*dx+dy*dy+dz*dz)/(px*px+py*py+pz*pz)); return d; }