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' -> gamma gamma pi0
10  class BESIII_2016_I1504943 : public Analysis {
11  public:
12
13    /// Constructor
14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2016_I1504943);
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==331);
24      declare(ufs, "UFS");
25      DecayedParticles ETA(ufs);
26      ETA.addStable(PID::PI0);
27      ETA.addStable(PID::K0S);
28      declare(ETA, "ETA");
29      // Book histograms
30      for(unsigned int ix=0;ix<3;++ix)
31	book(_h_br[ix],1,1,1+ix);
32      book(_h_m, 2, 1, 1);
33      book(_netap, "TMP/netap");
34    }
35
36    /// Perform the per-event analysis
37    void analyze(const Event& event) {
38      static const map<PdgId,unsigned int> & mode   = { {111,1}, { 22,2} };
39      DecayedParticles ETA = apply<DecayedParticles>(event, "ETA");
40      // loop over particles
41      for(unsigned int ix=0;ix<ETA.decaying().size();++ix) {
42	_netap->fill();
43	// select right decay mode
44	if ( !ETA.modeMatches(ix,3,mode)) continue;
45	const Particles & gam = ETA.decayProducts()[ix].at(22);
46	double mass2 = (gam[0].momentum()+gam[1].momentum()).mass2();
47	_h_m->fill(mass2);
48	_h_br[0]->fill();
49	if(any(ETA.decaying()[ix].children(), hasAbsPID(PID::OMEGA))) _h_br[1]->fill();
50	if(ETA.decaying()[ix].children().size()==3) _h_br[2]->fill();
51      }
52    }
53
54
55    /// Normalise histograms etc., after the run
56    void finalize() {
57      // eta' width in kev
58      double gammaEtap = 0.188e3;
59      scale(_h_m, gammaEtap/ *_netap);
60      for(unsigned int ix=0;ix<3;++ix)
61	scale(_h_br[ix], 1e4/ *_netap);
62    }
63
64    /// @}
65
66
67    /// @name Histograms
68    /// @{
69    Histo1DPtr _h_m;
70    CounterPtr _netap,_h_br[3];
71    /// @}
72
73
74  };
75
76
77  RIVET_DECLARE_PLUGIN(BESIII_2016_I1504943);
78
79}