Rivet analyses referenceBESIII_2021_I1966612Cross section for $e^+e^-\to$ neutron and antineutron between 2. and 3.08 GeVExperiment: BESIII (BEPC II) Inspire ID: 1966612 Status: VALIDATED Authors:
Beam energies: (1.0, 1.0); (1.0, 1.0); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.2, 1.2); (1.2, 1.2); (1.2, 1.2); (1.3, 1.3); (1.4, 1.4); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5) GeV Run details:
Measurement of the cross section for $e^+e^-\to p\bar{p}$ for energies between 2. and 3.08 GeV. Beam energy must be specified as analysis option "ENERGY" when rivet-merging samples. Source code: BESIII_2021_I1966612.cc 1// -*- C++ -*-
2#include "Rivet/Analysis.hh"
3#include "Rivet/Projections/FinalState.hh"
4
5namespace Rivet {
6
7
8 /// @brief e+ e- > n nbar
9 class BESIII_2021_I1966612 : public Analysis {
10 public:
11
12 /// Constructor
13 RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1966612);
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(FinalState(), "FS");
24
25 // Book histograms
26 book(_nneutron, 1, 1, 1);
27
28 for (const string& en : _nneutron.binning().edges<0>()) {
29 const double end = std::stod(en)*GeV;
30 if (isCompatibleWithSqrtS(end)) {
31 _ecms = en;
32 break;
33 }
34 }
35 if(_ecms.empty()) MSG_ERROR("Beam energy incompatible with analysis.");
36 }
37
38
39 /// Perform the per-event analysis
40 void analyze(const Event& event) {
41 const FinalState& fs = apply<FinalState>(event, "FS");
42 if(fs.particles().size()!=2) vetoEvent;
43 for (const Particle& p : fs.particles()) {
44 if(abs(p.pid())!=PID::NEUTRON) vetoEvent;
45 }
46 _nneutron->fill(_ecms);
47 }
48
49
50 /// Normalise histograms etc., after the run
51 void finalize() {
52 scale(_nneutron, crossSection()/ sumOfWeights() /picobarn);
53 }
54
55 ///@}
56
57
58 /// @name Histograms
59 ///@{
60 BinnedHistoPtr<string> _nneutron;
61 string _ecms;
62 ///@}
63
64
65 };
66
67
68 RIVET_DECLARE_PLUGIN(BESIII_2021_I1966612);
69
70}
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