1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/UnstableParticles.hh"
 4#include "Rivet/Projections/DecayedParticles.hh"
 5
 6namespace Rivet {
 7
 8
 9  /// @brief J/psi -> gamma eta' eta'
10  class BESIII_2022_I2016785 : public Analysis {
11  public:
12
13    /// Constructor
14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2016785);
15
16
17    /// @name Analysis methods
18    /// @{
19
20    /// Book histograms and initialise projections before the run
21    void init() {
22      UnstableParticles ufs = UnstableParticles(Cuts::pid==443);
23      declare(ufs, "UFS");
24      DecayedParticles psi(ufs);
25      psi.addStable(PID::PI0);
26      psi.addStable(PID::K0S);
27      psi.addStable(PID::ETA);
28      psi.addStable(PID::ETAPRIME);
29      declare(psi, "psi");
30      for(unsigned int ix=0;ix<2;++ix)
31	    book(_h[ix],1,1,1+ix);
32    }
33
34
35    /// Perform the per-event analysis
36    void analyze(const Event& event) {
37      static const map<PdgId,unsigned int> & mode   = { { 331,2} ,{22,1} };
38      DecayedParticles psi = apply<DecayedParticles>(event, "psi");
39      // loop over particles
40      for(unsigned int ix=0;ix<psi.decaying().size();++ix) {
41	if(!psi.modeMatches(ix,3,mode)) continue;
42	const Particles & eta   = psi.decayProducts()[ix].at( 331);
43	const Particle & gamma  = psi.decayProducts()[ix].at(  22)[0];
44	_h[0]->fill((eta[0].momentum()+eta[1].momentum()).mass());
45	for(unsigned int ix=0;ix<2;++ix)
46	  _h[1]->fill((gamma.momentum()+eta[ix].momentum()).mass());
47      }
48    }
49
50
51    /// Normalise histograms etc., after the run
52    void finalize() {
53      for(unsigned int ix=0;ix<2;++ix)
54	normalize(_h[ix],1.,false);
55    }
56
57    /// @}
58
59
60    /// @name Histograms
61    /// @{
62    Histo1DPtr _h[2];
63    /// @}
64
65
66  };
67
68
69  RIVET_DECLARE_PLUGIN(BESIII_2022_I2016785);
70
71}