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 Scatter2D temphisto(refData(1, 1, 1));
48 Scatter2DPtr mult;
49 book(mult, 1, 1, 1);
50 for (size_t b = 0; b < temphisto.numPoints(); b++) {
51 const double x = temphisto.point(b).x();
52 pair<double,double> ex = temphisto.point(b).xErrs();
53 pair<double,double> ex2 = ex;
54 if(ex2.first ==0.) ex2. first=0.0001;
55 if(ex2.second==0.) ex2.second=0.0001;
56 if (inRange(sqrtS()/GeV, x-ex2.first, x+ex2.second)) {
57 mult->addPoint(x, sigma, ex, make_pair(error,error));
58 }
59 else {
60 mult->addPoint(x, 0., ex, make_pair(0.,.0));
61 }
62 }
63 }
64
65 ///@}
66
67
68 /// @name Histograms
69 ///@{
70 CounterPtr _nneutron;
71 ///@}
72
73
74 };
75
76
77 RIVET_DECLARE_PLUGIN(BESIII_2021_I1966612);
78
79}
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