// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/DecayedParticles.hh"
namespace Rivet {
/// @brief eta -> pi0 gamma gamma
class A2_2014_I1297221 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(A2_2014_I1297221);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
UnstableParticles ufs = UnstableParticles(Cuts::pid==PID::ETA);
declare(ufs, "UFS");
DecayedParticles ETA(ufs);
ETA.addStable(PID::PI0);
ETA.addStable(PID::K0S);
declare(ETA, "ETA");
// histos
for(unsigned int ix=0;ix<3;++ix) book(_h[ix],1,1,1+ix);
book(_c,"TMP/nEta");
}
/// Perform the per-event analysis
void analyze(const Event& event) {
static const map<PdgId,unsigned int> & mode = { {111,1}, { 22,2} };
DecayedParticles ETA = apply<DecayedParticles>(event, "ETA");
// loop over particles
for(unsigned int ix=0;ix<ETA.decaying().size();++ix) {
_c->fill();
// select right decay mode
if ( !ETA.modeMatches(ix,3,mode)) continue;
const Particles & gam = ETA.decayProducts()[ix].at(22);
double mass2 = (gam[0].momentum()+gam[1].momentum()).mass2();
for(unsigned int ix=0;ix<3;++ix) _h[ix]->fill(mass2);
}
}
/// Normalise histograms etc., after the run
void finalize() {
// eta width in eV from PDG2022
double gam = 1.31e3;
for(unsigned int ix=0;ix<3;++ix) {
scale(_h[ix],gam / *_c);
}
}
/// @}
/// @name Histograms
/// @{
Histo1DPtr _h[3];
CounterPtr _c;
/// @}
};
RIVET_DECLARE_PLUGIN(A2_2014_I1297221);
}