1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/DecayedParticles.hh"
 4#include "Rivet/Projections/UnstableParticles.hh"
 5
 6namespace Rivet {
 7
 8
 9  /// @brief eta' -> pi+pi- gamma decay
10  class BESIII_2018_I1641075 : public Analysis {
11  public:
12
13    /// Constructor
14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1641075);
15
16
17    /// @name Analysis methods
18    /// @{
19
20    /// Book histograms and initialise projections before the run
21    void init() {
22
23      // Initialise and register projections
24      UnstableParticles ufs = UnstableParticles(Cuts::pid==331);
25      declare(ufs, "UFS");
26      DecayedParticles ETA(ufs);
27      ETA.addStable(PID::PI0);
28      declare(ETA, "ETA");
29
30      // Book histograms
31      book(_h_m, 1, 1, 5);
32
33    }
34
35    /// Perform the per-event analysis
36    void analyze(const Event& event) {
37      static const map<PdgId,unsigned int> & mode   = { { PID::PIPLUS,1}, { PID::PIMINUS ,1}, { PID::GAMMA,1}};
38      DecayedParticles ETA = apply<DecayedParticles>(event, "ETA");
39      // loop over particles
40      for(unsigned int ix=0;ix<ETA.decaying().size();++ix) {
41        if (!ETA.modeMatches(ix,3,mode)) continue;
42        const Particle & pip = ETA.decayProducts()[ix].at( PID::PIPLUS )[0];
43        const Particle & pim = ETA.decayProducts()[ix].at( PID::PIMINUS)[0];
44        _h_m->fill((pip.momentum()+pim.momentum()).mass());
45      }
46    }
47
48
49    /// Normalise histograms etc., after the run
50    void finalize() {
51      normalize(_h_m);
52    }
53
54    /// @}
55
56
57    /// @name Histograms
58    /// @{
59    Histo1DPtr _h_m;
60    /// @}
61
62
63  };
64
65
66  RIVET_DECLARE_PLUGIN(BESIII_2018_I1641075);
67
68
69}