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' -> pi+pi- e+e- decay
10  class BESIII_2020_I1830421 : public Analysis {
11  public:
12
13    /// Constructor
14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1830421);
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      declare(ETA,"ETA");
27      // Book histograms
28      //book(_h_mee  , 1, 1, 1);
29      book(_h_mpipi, 1, 1, 2);
30    }
31
32    /// Perform the per-event analysis
33    void analyze(const Event& event) {
34      static const map<PdgId,unsigned int> & mode = { { 211,1}, {-211,1}, { 11,1}, {-11,1}};
35      DecayedParticles ETA = apply<DecayedParticles>(event, "ETA");
36      // loop over particles
37      for(unsigned int ix=0;ix<ETA.decaying().size();++ix) {
38	  if (!ETA.modeMatches(ix,4,mode)) continue; 
39	  const Particle & pip = ETA.decayProducts()[ix].at( 211)[0];
40	  const Particle & pim = ETA.decayProducts()[ix].at(-211)[0];
41	  //const Particle & ep  = ETA.decayProducts()[ix].at(  11)[0];
42	  //const Particle & em  = ETA.decayProducts()[ix].at(- 11)[0];
43	  //_h_mee  ->fill((em .momentum()+ep .momentum()).mass());
44	  _h_mpipi->fill((pim.momentum()+pip.momentum()).mass());
45      }
46    }
47
48
49    /// Normalise histograms etc., after the run
50    void finalize() {
51      //normalize(_h_mee);
52      normalize(_h_mpipi);
53    }
54
55    /// @}
56
57
58    /// @name Histograms
59    /// @{
60    //Histo1DPtr _h_mee;
61    Histo1DPtr _h_mpipi;
62    /// @}
63
64
65  };
66
67
68  RIVET_DECLARE_PLUGIN(BESIII_2020_I1830421);
69
70}