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: ANY Run details:
Measurement of the cross section for $e^+e^-\to p\bar{p}$ for energies between 2. and 3.08 GeV. 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, "TMP/neutron");
27 }
28
29
30 /// Perform the per-event analysis
31 void analyze(const Event& event) {
32 const FinalState& fs = apply<FinalState>(event, "FS");
33 if(fs.particles().size()!=2) vetoEvent;
34 for (const Particle& p : fs.particles()) {
35 if(abs(p.pid())!=PID::NEUTRON) vetoEvent;
36 }
37 _nneutron->fill();
38 }
39
40
41 /// Normalise histograms etc., after the run
42 void finalize() {
43 double sigma = _nneutron->val();
44 double error = _nneutron->err();
45 sigma *= crossSection()/ sumOfWeights() /picobarn;
46 error *= crossSection()/ sumOfWeights() /picobarn;
47 Estimate1DPtr mult;
48 book(mult, 1, 1, 1);
49 for (auto& b : mult->bins()) {
50 if (inRange(sqrtS()/GeV, b.xMin(), b.xMax())) {
51 b.set(sigma, error);
52 }
53 }
54 }
55
56 ///@}
57
58
59 /// @name Histograms
60 ///@{
61 CounterPtr _nneutron;
62 ///@}
63
64
65 };
66
67
68 RIVET_DECLARE_PLUGIN(BESIII_2021_I1966612);
69
70}
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