// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/DecayedParticles.hh"
namespace Rivet {
/// @brief J/psi -> eta' e+e-
class BESIII_2019_I1692688 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2019_I1692688);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
UnstableParticles ufs = UnstableParticles(Cuts::abspid==PID::JPSI);
declare(ufs, "UFS");
DecayedParticles psi(ufs);
psi.addStable(PID::PI0);
psi.addStable(PID::ETAPRIME);
declare(psi, "PSI");
for(unsigned int ix=0;ix<2;++ix)
book(_h[ix], 1, 1, ix+1);
}
/// Perform the per-event analysis
void analyze(const Event& event) {
// define the decay mode
static const map<PdgId,unsigned int> & mode = { {PID::ETAPRIME,1},{ 11,1}, { -11,1}};
DecayedParticles psi = apply<DecayedParticles>(event, "PSI");
// loop over particles
for(unsigned int ix=0;ix<psi.decaying().size();++ix) {
if(!psi.modeMatches(ix,3,mode)) continue;
const Particle & em = psi.decayProducts()[ix].at( 11)[0];
const Particle & ep = psi.decayProducts()[ix].at(-11)[0];
double mee = (ep.momentum()+em.momentum()).mass();
for(unsigned int ix=0;ix<2;++ix) _h[ix]->fill(mee);
}
}
/// Normalise histograms etc., after the run
void finalize() {
for(unsigned int ix=0;ix<2;++ix)
normalize(_h[ix],1.,false);
}
/// @}
/// @name Histograms
/// @{
Histo1DPtr _h[2];
/// @}
};
RIVET_DECLARE_PLUGIN(BESIII_2019_I1692688);
}