1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/UnstableParticles.hh"
 4
 5namespace Rivet {
 6
 7
 8  /// @brief J/psi production at low energies
 9  class BESIII_2021_I1908066 : public Analysis {
10  public:
11
12    /// Constructor
13    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1908066);
14
15
16    /// @name Analysis methods
17    ///@{
18
19    /// Book histograms and initialise projections before the run
20    void init() {
21
22      // Initialise and register projections
23      declare(UnstableParticles(), "UFS");
24      book(_c_psi   , 1, 1, 1);
25
26      for (const string& en : _c_psi.binning().edges<0>()) {
27        const double end = std::stod(en)*GeV;
28        if (isCompatibleWithSqrtS(end)) {
29          _ecms = en;
30          break;
31        }
32      }
33      if (_ecms.empty()) MSG_ERROR("Beam energy incompatible with analysis.");
34    }
35
36
37    /// Perform the per-event analysis
38    void analyze(const Event& event) {
39      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
40      unsigned int count = ufs.particles(Cuts::pid==443).size();
41      _c_psi->fill(_ecms,count);
42    }
43
44
45    /// Normalise histograms etc., after the run
46    void finalize() {
47      scale(_c_psi, crossSection()/nanobarn/sumOfWeights());
48    }
49
50    ///@}
51
52
53    /// @name Histograms
54    ///@{
55    BinnedHistoPtr<string> _c_psi;
56    string _ecms;
57    ///@}
58
59
60  };
61
62
63  RIVET_DECLARE_PLUGIN(BESIII_2021_I1908066);
64
65}