Rivet analyses referenceSND_2022_I2102082Cross section for $e^+e^-\to n\bar{n}$ between threshold and 2 GeVExperiment: SND (VEPP-2M) Inspire ID: 2102082 Status: VALIDATED NOHEPDATA Authors:
Beam energies: (0.9, 0.9); (0.9, 0.9); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0) GeV Run details:
Measurement of the cross section for $e^+e^-\to n\bar{n}$ at energies between threshold and 2 GeV. Beam energy must be specified as analysis option "ENERGY" when rivet-merging samples. Source code: SND_2022_I2102082.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 SND_2022_I2102082 : public Analysis {
10 public:
11
12 /// Constructor
13 RIVET_DEFAULT_ANALYSIS_CTOR(SND_2022_I2102082);
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 double end = std::stod(en)*MeV;
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() /nanobarn);
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(SND_2022_I2102082);
69
70}
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