// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
namespace Rivet {
/// @brief J/psi -> 3 gamma
class BESIII_2013_I1126137 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2013_I1126137);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// projections
declare(UnstableParticles(Cuts::pid==443), "UFS");
// histos
book(_h,1,1,1);
book(_c,"TMP/nJPsi");
}
/// Perform the per-event analysis
void analyze(const Event& event) {
// Find the J/psi among the unstables
for (const Particle& psi : apply<UnstableParticles>(event, "UFS").particles()) {
_c->fill();
unsigned int nhadron(0);
Particles photons;
for(const Particle & child : psi.children()) {
if(PID::isHadron(child.pid()))
++nhadron;
else if(child.pid()==PID::PHOTON)
photons.push_back(child);
}
if(nhadron==0 && photons.size()==3) {
LorentzTransform boost;
if (psi.p3().mod() > 1*MeV)
boost = LorentzTransform::mkFrameTransformFromBeta(psi.momentum().betaVec());
for(const Particle & gamma:photons)
_h->fill(2.*boost.transform(gamma.momentum()).E()/psi.mass());
}
}
}
/// Normalise histograms etc., after the run
void finalize() {
scale(_h, 1e6/3. / *_c);
}
/// @}
/// @name Histograms
/// @{
Histo1DPtr _h;
CounterPtr _c;
/// @}
};
RIVET_DECLARE_PLUGIN(BESIII_2013_I1126137);
}