Rivet analyses

Cross section for e+e− → π+π− 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: (0.2, 0.2); (0.2, 0.2); (0.2, 0.2); (0.2, 0.2); (0.2, 0.2); (0.2, 0.2); (0.2, 0.2); (0.2, 0.2); (0.3, 0.3); (0.3, 0.3)GeV

Run details: - e+ e- to hadrons below 0.6 and 0.9 GeV

Measurement of the cross section for e+e− → π+π− at energies between 370 and 520 MeV. Useful for comparing models of the pion form factor.

Source code:CMD2_2006_I728191.cc

// -*- 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
    RIVET_DEFAULT_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, 3,1,1);
      for (double eVal : allowedEnergies()) {
        int en = round(eVal/MeV);
        if (isCompatibleWithSqrtS(eVal)) {
          _sqs = en; break;
        }
      }
      raiseBeamErrorIf(_sqs < 0);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const FinalState& fs = apply<FinalState>(event, "FS");
      if (fs.particles().size() != 2) vetoEvent;
      for (const Particle& p : fs.particles()) {
        if (p.abspid() != PID::PIPLUS) vetoEvent;
      }
      _npion->fill(_sqs);
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_npion,crossSection()/sumOfWeights()/nanobarn);
    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<int> _npion;
    int _sqs = -1;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(CMD2_2006_I728191);
}