1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/FinalState.hh"
 4
 5namespace Rivet {
 6
 7
 8  /// @brief 
 9  class BESIII_2020_I1808875 : public Analysis {
10  public:
11
12    /// Constructor
13    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1808875);
14
15
16    /// @name Analysis methods
17    /// @{
18
19    /// Book histograms and initialise projections before the run
20    void init() {
21      // Projections
22      declare(FinalState(), "FS");
23      book(_sigma_muons, 1,1,1);
24      for (const string& en : _sigma_muons.binning().edges<0>()) {
25        const double end = std::stod(en)*GeV;
26        if (isCompatibleWithSqrtS(end)) {
27          _ecms = en;
28          break;
29        }
30      }
31      if (_ecms.empty()) MSG_ERROR("Beam energy incompatible with analysis.");
32    }
33
34
35    /// Perform the per-event analysis
36    void analyze(const Event& event) {
37      const FinalState& fs = apply<FinalState>(event, "FS");
38
39      map<long,int> nCount;
40      int ntotal(0);
41      for (const Particle& p : fs.particles()) {
42        nCount[p.pid()] += 1;
43        ++ntotal;
44      }
45      // mu+mu- + photons
46      if (nCount[-13]==1 && nCount[13]==1 && ntotal==2+nCount[22]) {
47        _sigma_muons->fill(_ecms);
48      }
49    }
50
51
52    /// Normalise histograms etc., after the run
53    void finalize() {
54      scale(_sigma_muons, crossSection()/ sumOfWeights() /nanobarn);
55    }
56
57    /// @}
58
59
60    /// @name Histograms
61    /// @{
62    BinnedHistoPtr<string> _sigma_muons;
63    string _ecms;
64    /// @}
65
66
67  };
68
69
70  RIVET_DECLARE_PLUGIN(BESIII_2020_I1808875);
71
72}