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SND_2014_I1321689

Cross section for $e^+e^-\to n\bar{n}$ between threshold and 2 GeV
Experiment: SND (VEPP-2M)
Inspire ID: 1321689
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Rev. D90 (2014) 112007, 2014
Beams: e+ e-
Beam energies: ANY
Run details:
  • e+e- to hadrons

Source code: SND_2014_I1321689.cc
 1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/FinalState.hh"
 4
 5
 6namespace Rivet {
 7
 8
 9  /// @brief Add a short analysis description here
10  class SND_2014_I1321689 : public Analysis {
11  public:
12
13    /// Constructor
14    RIVET_DEFAULT_ANALYSIS_CTOR(SND_2014_I1321689);
15
16
17    /// @name Analysis methods
18    //@{
19
20    /// Book histograms and initialise projections before the run
21    void init() {
22
23      // Initialise and register projections
24      declare(FinalState(), "FS");
25
26      // Book histograms
27      book(_nneutron, "TMP/neutron");
28
29    }
30
31
32    /// Perform the per-event analysis
33    void analyze(const Event& event) {
34      const FinalState& fs = apply<FinalState>(event, "FS");
35      if(fs.particles().size()!=2) vetoEvent;
36      for (const Particle& p : fs.particles()) {
37	if(abs(p.pid())!=PID::NEUTRON) vetoEvent;
38      }
39      _nneutron->fill();
40    }
41
42
43    /// Normalise histograms etc., after the run
44    void finalize() {
45
46      double sigma = _nneutron->val();
47      double error = _nneutron->err();
48      sigma *= crossSection()/ sumOfWeights() /nanobarn;
49      error *= crossSection()/ sumOfWeights() /nanobarn;
50      for(unsigned int ix=1;ix<3;++ix) {
51	Scatter2D temphisto(refData(ix, 1, 1));
52	Scatter2DPtr mult;
53	book(mult, ix, 1, 1);
54	for (size_t b = 0; b < temphisto.numPoints(); b++) {
55	  const double x  = temphisto.point(b).x();
56	  pair<double,double> ex = temphisto.point(b).xErrs();
57	  pair<double,double> ex2 = ex;
58	  if(ex2.first ==0.) ex2. first=0.0001;
59	  if(ex2.second==0.) ex2.second=0.0001;
60	  if (inRange(sqrtS()/MeV, x-ex2.first, x+ex2.second)) {
61	    mult->addPoint(x, sigma, ex, make_pair(error,error));
62	  }
63	  else {
64	    mult->addPoint(x, 0., ex, make_pair(0.,.0));
65	  }
66	}
67      }
68
69    }
70
71    //@}
72
73
74    /// @name Histograms
75    //@{
76    CounterPtr _nneutron;
77    //@}
78
79
80  };
81
82
83  // The hook for the plugin system
84  RIVET_DECLARE_PLUGIN(SND_2014_I1321689);
85
86
87}