// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/DecayedParticles.hh"
namespace Rivet {
/// @brief eta' -> pi+pi- e+e- decay
class BESIII_2020_I1830421 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1830421);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
UnstableParticles ufs = UnstableParticles(Cuts::pid== 331);
declare(ufs, "UFS");
DecayedParticles ETA(ufs);
declare(ETA,"ETA");
// Book histograms
//book(_h_mee , 1, 1, 1);
book(_h_mpipi, 1, 1, 2);
}
/// Perform the per-event analysis
void analyze(const Event& event) {
static const map<PdgId,unsigned int> & mode = { { 211,1}, {-211,1}, { 11,1}, {-11,1}};
DecayedParticles ETA = apply<DecayedParticles>(event, "ETA");
// loop over particles
for(unsigned int ix=0;ix<ETA.decaying().size();++ix) {
if (!ETA.modeMatches(ix,4,mode)) continue;
const Particle & pip = ETA.decayProducts()[ix].at( 211)[0];
const Particle & pim = ETA.decayProducts()[ix].at(-211)[0];
//const Particle & ep = ETA.decayProducts()[ix].at( 11)[0];
//const Particle & em = ETA.decayProducts()[ix].at(- 11)[0];
//_h_mee ->fill((em .momentum()+ep .momentum()).mass());
_h_mpipi->fill((pim.momentum()+pip.momentum()).mass());
}
}
/// Normalise histograms etc., after the run
void finalize() {
//normalize(_h_mee);
normalize(_h_mpipi);
}
/// @}
/// @name Histograms
/// @{
//Histo1DPtr _h_mee;
Histo1DPtr _h_mpipi;
/// @}
};
RIVET_DECLARE_PLUGIN(BESIII_2020_I1830421);
}