1 //--------------------------------------------------------------------------
4 // This software is part of the EvtGen package developed jointly
5 // for the BaBar and CLEO collaborations. If you use all or part
6 // of it, please give an appropriate acknowledgement.
8 // Copyright Information: See EvtGen/COPYRIGHT
9 // Copyright (C) 1998 Caltech, UCSB
11 // Module: EvtPi0Dalitz.cc
13 // Description: pi0 -> e+ e- gamma
15 // Modification history:
17 // DJL/RYD June 30, 1998 Module created
19 //------------------------------------------------------------------------
21 #include "EvtGenBase/EvtPatches.hh"
26 #include "EvtGenBase/EvtGenKine.hh"
27 #include "EvtGenBase/EvtParticle.hh"
28 #include "EvtGenBase/EvtPDL.hh"
29 #include "EvtGenBase/EvtReport.hh"
30 #include "EvtGenModels/EvtEta2MuMuGamma.hh"
31 #include "EvtGenBase/EvtVector4C.hh"
32 #include "EvtGenBase/EvtDiracSpinor.hh"
33 #include "EvtGenBase/EvtVector4C.hh"
34 #include "EvtGenBase/EvtTensor4C.hh"
37 EvtEta2MuMuGamma::~EvtEta2MuMuGamma() {}
39 std::string EvtEta2MuMuGamma::getName(){
41 return "ETA2MUMUGAMMA";
45 EvtDecayBase* EvtEta2MuMuGamma::clone(){
47 return new EvtEta2MuMuGamma;
52 void EvtEta2MuMuGamma::initProbMax(){
59 void EvtEta2MuMuGamma::init(){
61 // check that there are 0 arguments
66 checkSpinParent(EvtSpinType::SCALAR);
68 checkSpinDaughter(0,EvtSpinType::DIRAC);
69 checkSpinDaughter(1,EvtSpinType::DIRAC);
70 checkSpinDaughter(2,EvtSpinType::PHOTON);
75 void EvtEta2MuMuGamma::decay( EvtParticle *p){
77 EvtParticle *ep, *em, *gamma;
78 setWeight(p->initializePhaseSpace(getNDaug(),getDaugs(),false,
85 // the next four lines generates events with a weight such that
86 // the efficiency for selecting them is good. The parameter below of
87 // 0.1 is the size of the peak at low q^2 (in arbitrary units).
88 // The value of 0.1 is appropriate for muons.
89 // when you use this remember to remove the cut on q^2!
92 //ep em invariant mass^2
93 double m2=(ep->getP4()+em->getP4()).mass2();
94 EvtVector4R q=ep->getP4()+em->getP4();
95 //Just use the prob summed over spins...
99 v=2.0*(gamma->getP4()*q)*EvtGenFunctions::directProd(q,gamma->getP4())
100 - (gamma->getP4()*q)*(gamma->getP4()*q)*EvtTensor4C::g()
101 -m2*EvtGenFunctions::directProd(gamma->getP4(),gamma->getP4());
103 w=4.0*( EvtGenFunctions::directProd(ep->getP4(),em->getP4()) +
104 EvtGenFunctions::directProd(em->getP4(),ep->getP4())
105 -EvtTensor4C::g()*(ep->getP4()*em->getP4()-ep->getP4().mass2()));
107 double prob=(real(cont(v,w)))/(m2*m2);
108 prob *=(1.0/( (0.768*0.768-m2)*(0.768*0.768-m2)
109 +0.768*0.768*0.151*0.151));
111 // report(INFO,"EvtGen") << "prob is "<<prob<<endl;