// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/DecayedParticles.hh"
namespace Rivet {
/// @brief D0 -> eta eta pi0
class BESIII_2018_I1662665 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1662665);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
UnstableParticles ufs = UnstableParticles(Cuts::abspid==421);
declare(ufs, "UFS");
DecayedParticles D0(ufs);
D0.addStable(PID::PI0);
D0.addStable(PID::K0S);
D0.addStable(PID::ETA);
D0.addStable(PID::ETAPRIME);
declare(D0, "D0");
// histograms
book(_h_pieta,1,1,1);
book(_dalitz,"dalitz",50.,0.4,1.6,50,0.4,1.8);
}
/// Perform the per-event analysis
void analyze(const Event& event) {
// define the decay mode
static const map<PdgId,unsigned int> & mode = { { 221,2}, {111,1}};
DecayedParticles D0 = apply<DecayedParticles>(event, "D0");
// loop over particles
for(unsigned int ix=0;ix<D0.decaying().size();++ix) {
if ( ! D0.modeMatches(ix,3,mode)) continue;
const Particles & eta = D0.decayProducts()[ix].at(221);
const Particles & pi0 = D0.decayProducts()[ix].at(111);
double m1 = (eta[0].momentum()+pi0[0].momentum()).mass2();
double m2 = (eta[1].momentum()+pi0[0].momentum()).mass2();
if(m1>m2) swap(m1,m2);
_dalitz->fill(m1,m2);
_h_pieta->fill(sqrt(m1));
_h_pieta->fill(sqrt(m2));
}
}
/// Normalise histograms etc., after the run
void finalize() {
normalize(_h_pieta);
normalize(_dalitz);
}
/// @}
/// @name Histograms
/// @{
Histo1DPtr _h_pieta;
Histo2DPtr _dalitz;
/// @}
};
RIVET_DECLARE_PLUGIN(BESIII_2018_I1662665);
}