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' pi+pi-
10  class BESIII_2016_I1437949 : public Analysis {
11  public:
12
13    /// Constructor
14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2016_I1437949);
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::abspid==443);
24      declare(ufs, "UFS");
25      DecayedParticles PSI(ufs);
26      PSI.addStable(PID::ETA);
27      PSI.addStable(PID::ETAPRIME);
28      declare(PSI, "PSI");
29      // histos
30      for(unsigned int ix=0;ix<2;++ix)
31	book(_h[ix],1,1,1+ix);
32      book(_h[2],2,1,1);
33    }
34
35
36    /// Perform the per-event analysis
37    void analyze(const Event& event) {
38      // find the J/psi decays
39      static const map<PdgId,unsigned int> & mode = { { 22,1}, { 331,1}, {211,1}, {-211,1}};
40      DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
41      for(unsigned int ix=0;ix<PSI.decaying().size();++ix) {
42	if(!PSI.modeMatches(ix,4,mode)) continue;
43	const Particle  & gam  = PSI.decayProducts()[ix].at( 22)[0];
44	double mass =(PSI.decaying()[ix].momentum()-gam.momentum()).mass() ;
45	for(unsigned int ix=0;ix<3;++ix) _h[ix]->fill(mass);
46      }
47    }
48
49
50    /// Normalise histograms etc., after the run
51    void finalize() {
52      for(unsigned int ix=0;ix<3;++ix)
53	normalize(_h[ix],1.,false);
54    }
55
56    /// @}
57
58
59    /// @name Histograms
60    /// @{
61    Histo1DPtr _h[3];
62    /// @}
63
64
65  };
66
67
68  RIVET_DECLARE_PLUGIN(BESIII_2016_I1437949);
69
70}