1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/FinalState.hh"
 4
 5
 6namespace Rivet {
 7
 8
 9  /// @brief Cross section for $e^+e^-\to \pi^+\pi^-$ between 0.6 and 0.9 GeV
10  class BESIII_2016_I1385603 : public Analysis {
11  public:
12
13    /// Constructor
14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2016_I1385603);
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      declare(FinalState(), "FS");
25
26      // Book histograms
27      book(_npion, "TMP/pion");
28
29    }
30
31
32    /// Perform the per-event analysis
33    void analyze(const Event& event) {
34      const FinalState& fs = apply<FinalState>(event, "FS");
35      if(fs.particles().size()!=2) vetoEvent;
36      for (const Particle& p : fs.particles()) {
37        if(abs(p.pid())!=PID::PIPLUS) vetoEvent;
38      }
39      _npion->fill();
40    }
41
42
43    /// Normalise histograms etc., after the run
44    void finalize() {
45      double sigma = _npion->val();
46      double error = _npion->err();
47      sigma *= crossSection()/ sumOfWeights() /nanobarn;
48      error *= crossSection()/ sumOfWeights() /nanobarn;
49      Estimate1DPtr  mult;
50      book(mult, 1, 1, 1);
51      for (auto& b : mult->bins()) {
52        if (inRange(sqrtS()/GeV, b.xMin(), b.xMax())) {
53          b.set(sigma, error);
54        }
55      }
56    }
57
58    /// @}
59
60
61    /// @name Histograms
62    /// @{
63    CounterPtr _npion;
64    /// @}
65
66
67  };
68
69
70  RIVET_DECLARE_PLUGIN(BESIII_2016_I1385603);
71
72
73}