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## Rivet analyses reference

### 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 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 // -*- C++ -*- #include "Rivet/Analysis.hh" #include "Rivet/Projections/FinalState.hh" namespace Rivet { /// @brief Add a short analysis description here class CMD2_2006_I728191 : public Analysis { public: /// Constructor DEFAULT_RIVET_ANALYSIS_CTOR(CMD2_2006_I728191); /// @name Analysis methods //@{ /// Book histograms and initialise projections before the run void init() { // Initialise and register projections declare(FinalState(), "FS"); // Book histograms book(_npion, "TMP/pion"); } /// Perform the per-event analysis void analyze(const Event& event) { const FinalState& fs = apply(event, "FS"); if(fs.particles().size()!=2) vetoEvent; for (const Particle& p : fs.particles()) { if(abs(p.pid())!=PID::PIPLUS) vetoEvent; } _npion->fill(); } /// Normalise histograms etc., after the run void finalize() { Scatter2D temphisto(refData(3, 1, 1)); double sigma = _npion->val(); double error = _npion->err(); sigma *= crossSection()/ sumOfWeights() /nanobarn; error *= crossSection()/ sumOfWeights() /nanobarn; Scatter2DPtr mult; book(mult, 3, 1, 1); for (size_t b = 0; b < temphisto.numPoints(); b++) { const double x = temphisto.point(b).x(); pair ex = temphisto.point(b).xErrs(); pair ex2 = ex; if(ex2.first ==0.) ex2. first=0.0001; if(ex2.second==0.) ex2.second=0.0001; if (inRange(sqrtS()/MeV, x-ex2.first, x+ex2.second)) { mult->addPoint(x, sigma, ex, make_pair(error,error)); } else { mult->addPoint(x, 0., ex, make_pair(0.,.0)); } } } //@} /// @name Histograms //@{ CounterPtr _npion; //@} }; // The hook for the plugin system DECLARE_RIVET_PLUGIN(CMD2_2006_I728191); }