Rivet analyses

Cross section for e+e− → πγ for energies between 1.075 GeV and 2 GeV

Experiment: SND (VEPP-2M)

Inspire ID: 1694988

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 1809.07631

Beams: e+ e-

Beam energies: ANY

Run details: - e+ e- to hadrons

Cross section for e+e− → πγ for energies between 1.075 GeV and 2 GeV

Source code:SND_2018_I1694988.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"

namespace Rivet {


  /// @brief e+e- -> pi0 gamma
  class SND_2018_I1694988 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(SND_2018_I1694988);


    /// @name Analysis methods
    /// @{

    /// Book histograms and initialise projections before the run
    void init() {
      declare(FinalState(), "FS");
      book(_numPi0Gamma, 1, 1, 1);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {

      const FinalState& fs = apply<FinalState>(event, "FS");

      map<long,int> nCount;
      int ntotal(0);
      for (const Particle& p : fs.particles()) {
    nCount[p.pid()] += 1;
    ++ntotal;
      }
      if(ntotal==2 && nCount[22]==1 && nCount[111]==1)
    _numPi0Gamma->fill(round(sqrtS()/MeV));
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_numPi0Gamma, crossSection()/ sumOfWeights() /picobarn);
    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<int> _numPi0Gamma;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(SND_2018_I1694988);


}