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CMD2_2006_I728191

Cross section for $e^+e^-\to \pi^+\pi^-$ between 370 and 520 MeV
Experiment: CMD2 (VEPP-2M)
Inspire ID: 728191
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • JETP Lett. 84 (2006) 413-417, 2006
Beams: e+ e-
Beam energies: ANY
Run details:
  • e+ e- to hadrons below 0.6 and 0.9 GeV

Measurement of the cross section for $e^+e^-\to \pi^+\pi^-$ at energies between 370 and 520 MeV. Useful for comparing models of the pion form factor.

Source code: CMD2_2006_I728191.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 CMD2_2006_I728191 : public Analysis {
11  public:
12
13    /// Constructor
14    RIVET_DEFAULT_ANALYSIS_CTOR(CMD2_2006_I728191);
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(_npion, "TMP/pion");
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::PIPLUS) vetoEvent;
38      }
39      _npion->fill();
40    }
41
42
43    /// Normalise histograms etc., after the run
44    void finalize() {
45      Scatter2D temphisto(refData(3, 1, 1));
46      double sigma = _npion->val();
47      double error = _npion->err();
48      sigma *= crossSection()/ sumOfWeights() /nanobarn;
49      error *= crossSection()/ sumOfWeights() /nanobarn; 
50      Scatter2DPtr mult;
51      book(mult, 3, 1, 1);
52      for (size_t b = 0; b < temphisto.numPoints(); b++) {
53	const double x  = temphisto.point(b).x();
54	pair<double,double> ex = temphisto.point(b).xErrs();
55	pair<double,double> ex2 = ex;
56	if(ex2.first ==0.) ex2. first=0.0001;
57	if(ex2.second==0.) ex2.second=0.0001;
58	if (inRange(sqrtS()/MeV, x-ex2.first, x+ex2.second)) {
59	  mult->addPoint(x, sigma, ex, make_pair(error,error));
60	}
61	else {
62	  mult->addPoint(x, 0., ex, make_pair(0.,.0));
63	}
64      }
65    }
66
67    //@}
68
69
70    /// @name Histograms
71    //@{
72    CounterPtr _npion;
73    //@}
74
75
76  };
77
78
79  // The hook for the plugin system
80  RIVET_DECLARE_PLUGIN(CMD2_2006_I728191);
81
82
83}