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 eta -> pi0 gamma gamma
10  class A2_2014_I1297221 : public Analysis {
11  public:
12
13    /// Constructor
14    RIVET_DEFAULT_ANALYSIS_CTOR(A2_2014_I1297221);
15
16
17    /// @name Analysis methods
18    /// @{
19
20    /// Book histograms and initialise projections before the run
21    void init() {
22      // Initialise and register projections
23      UnstableParticles ufs = UnstableParticles(Cuts::pid==PID::ETA);
24      declare(ufs, "UFS");
25      DecayedParticles ETA(ufs);
26      ETA.addStable(PID::PI0);
27      ETA.addStable(PID::K0S);
28      declare(ETA, "ETA");
29      // histos
30      for(unsigned int ix=0;ix<3;++ix) book(_h[ix],1,1,1+ix);
31      book(_c,"TMP/nEta");
32    }
33
34
35    /// Perform the per-event analysis
36    void analyze(const Event& event) {
37      static const map<PdgId,unsigned int> & mode   = { {111,1}, { 22,2} };
38      DecayedParticles ETA = apply<DecayedParticles>(event, "ETA");
39      // loop over particles
40      for(unsigned int ix=0;ix<ETA.decaying().size();++ix) {
41	_c->fill();
42	// select right decay mode
43	if ( !ETA.modeMatches(ix,3,mode)) continue;
44	const Particles & gam = ETA.decayProducts()[ix].at(22);
45	double mass2 = (gam[0].momentum()+gam[1].momentum()).mass2();
46	for(unsigned int ix=0;ix<3;++ix) _h[ix]->fill(mass2);
47      }
48    }
49
50
51    /// Normalise histograms etc., after the run
52    void finalize() {
53      // eta width in eV from PDG2022
54      double gam = 1.31e3;
55      for(unsigned int ix=0;ix<3;++ix) {
56	scale(_h[ix],gam / *_c);
57      }
58    }
59
60    /// @}
61
62
63    /// @name Histograms
64    /// @{
65    Histo1DPtr _h[3];
66    CounterPtr _c;
67    /// @}
68
69
70  };
71
72
73  RIVET_DECLARE_PLUGIN(A2_2014_I1297221);
74
75}