Rivet analyses referenceSND_2024_I2809929Cross section for $e^+e^-\to n\bar{n}$ near thresholdExperiment: SND (VEPP-2000) Inspire ID: 2809929 Status: VALIDATED NOHEPDATA Authors:
Beam energies: (0.9, 0.9); (0.9, 0.9); (0.9, 0.9); (0.9, 0.9); (0.9, 0.9); (0.9, 0.9); (0.9, 0.9); (0.9, 0.9); (0.9, 0.9); (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 near the threshold. Beam energy must be specified as analysis option "ENERGY" when rivet-merging samples. Source code: SND_2024_I2809929.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_2024_I2809929 : public Analysis {
10 public:
11
12 /// Constructor
13 RIVET_DEFAULT_ANALYSIS_CTOR(SND_2024_I2809929);
14
15 /// @name Analysis methods
16 /// @{
17
18 /// Book histograms and initialise projections before the run
19 void init() {
20
21 // Initialise and register projections
22 declare(FinalState(), "FS");
23
24 // Book histograms
25 book(_nneutron, 1, 1, 1);
26
27 for (const string& en : _nneutron.binning().edges<0>()) {
28 double end = 2.*std::stod(en)*MeV;
29 if(isCompatibleWithSqrtS(end)) {
30 _ecms = en;
31 break;
32 }
33 }
34 if(_ecms.empty()) MSG_ERROR("Beam energy incompatible with analysis.");
35 }
36
37
38 /// Perform the per-event analysis
39 void analyze(const Event& event) {
40 const FinalState& fs = apply<FinalState>(event, "FS");
41 if (fs.particles().size()!=2) vetoEvent;
42 for (const Particle& p : fs.particles()) {
43 if(abs(p.pid())!=PID::NEUTRON) vetoEvent;
44 }
45 _nneutron->fill(_ecms);
46 }
47
48
49 /// Normalise histograms etc., after the run
50 void finalize() {
51 scale(_nneutron, crossSection()/ sumOfWeights() /nanobarn);
52
53 }
54
55 /// @}
56
57 /// @name Histograms
58 /// @{
59 BinnedHistoPtr<string> _nneutron;
60 string _ecms;
61 /// @}
62
63 };
64
65
66 RIVET_DECLARE_PLUGIN(SND_2024_I2809929);
67
68}
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