// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/Beam.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/DecayedParticles.hh"
namespace Rivet {
/// @brief Jpsi -> gamma gamma phi
class BESIII_2018_I1646687 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1646687);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
UnstableParticles ufs = UnstableParticles(Cuts::abspid==443);
declare(ufs, "UFS");
DecayedParticles PSI(ufs);
PSI.addStable(PID::PHI);
declare(PSI, "PSI");
declare(Beam(), "Beams");
book(_h_mass,1,1,1);
for(unsigned int ix=0;ix<2;++ix) {
book(_h_angle[ix],2,1,1+ix);
}
}
/// Perform the per-event analysis
void analyze(const Event& event) {
// get the axis, direction of incoming electron
const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
Vector3 axis;
if(beams.first.pid()>0)
axis = beams.first .momentum().p3().unit();
else
axis = beams.second.momentum().p3().unit();
// find the J/psi decays
static const map<PdgId,unsigned int> & mode = { { 22,2},{ 333,1}};
DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
if( PSI.decaying().size()!=1) vetoEvent;
if(!PSI.modeMatches(0,3,mode)) vetoEvent;
// particles
const Particle & phi = PSI.decayProducts()[0].at(333)[0];
const Particles & gam = PSI.decayProducts()[0].at( 22);
for(unsigned int ix=0;ix<2;++ix) {
double mPhiGamma = (gam[ix].momentum()+phi.momentum()).mass();
_h_mass->fill(mPhiGamma);
double cTheta = axis.dot(gam[ix==0 ? 1 : 0].p3().unit());
if(mPhiGamma>1.4 && mPhiGamma<1.6)
_h_angle[0]->fill(cTheta);
else if(mPhiGamma>1.75 && mPhiGamma<1.9)
_h_angle[1]->fill(cTheta);
}
}
/// Normalise histograms etc., after the run
void finalize() {
normalize(_h_mass,1.,false);
for(unsigned int ix=0;ix<2;++ix) {
normalize(_h_angle[ix],1.,false);
}
}
/// @}
/// @name Histograms
/// @{
Histo1DPtr _h_mass, _h_angle[2];
/// @}
};
RIVET_DECLARE_PLUGIN(BESIII_2018_I1646687);
}