1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/FinalState.hh"
 4#include "Rivet/Projections/FastJets.hh"
 5#include "Rivet/Projections/LeptonFinder.hh"
 6#include "Rivet/Projections/MissingMomentum.hh"
 7#include "Rivet/Projections/PromptFinalState.hh"
 8
 9namespace Rivet {
10
11
12  /// @brief e+e- > 2p 2pbar
13  class BESIII_2020_I1837725 : public Analysis {
14  public:
15
16    /// Constructor
17    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1837725);
18
19
20    /// @name Analysis methods
21    ///@{
22
23    /// Book histograms and initialise projections before the run
24    void init() {
25
26      // Initialise and register projections
27      declare(FinalState(), "FS");
28
29      // Book histograms
30      book(_nproton, "TMP/proton");
31    }
32
33
34    /// Perform the per-event analysis
35    void analyze(const Event& event) {
36      const FinalState& fs = apply<FinalState>(event, "FS");
37      if(fs.particles().size()!=4) vetoEvent;
38      for (const Particle& p :  fs.particles()) {
39	if(abs(p.pid())!=PID::PROTON) vetoEvent;
40      }
41      _nproton->fill();
42    }
43
44
45    /// Normalise histograms etc., after the run
46    void finalize() {
47      double sigma = _nproton->val();
48      double error = _nproton->err();
49      sigma *= crossSection()/ sumOfWeights() /femtobarn;
50      error *= crossSection()/ sumOfWeights() /femtobarn;
51      Estimate1DPtr  mult;
52      book(mult, 1, 1, 1);
53      for (auto& b : mult->bins()) {
54        if (inRange(sqrtS()/GeV, b.xMin(), b.xMax())) {
55          b.set(sigma, error);
56        }
57      }
58    }
59
60    ///@}
61
62
63    /// @name Histograms
64    ///@{
65    CounterPtr _nproton;
66    ///@}
67
68
69  };
70
71
72  RIVET_DECLARE_PLUGIN(BESIII_2020_I1837725);
73
74}