Rivet analyses

Cross section for e+e− → π+π+π−π+ below 1 GeV

Experiment: CMD2 (VEPP-2M)

Inspire ID: 511375

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett. B475 (2000) 190-197, 2000

Beams: e+ e-

Beam energies: ANY

Run details: - e+e- to hadrons

Measurement of the cross section for e+e− → π+π+π−π+ below 1 GeV

Source code:CMD2_2000_I511375.cc

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

namespace Rivet {


  /// @brief e+e- > pi+pi-
  class CMD2_2000_I511375 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CMD2_2000_I511375);


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

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      declare(FinalState(), "FS");

      // Book histograms
      book(_npion, 1, 1, 1);
      for (const string& en : _npion.binning().edges<0>()) {
        const size_t idx = en.find("-");
        if (idx != string::npos) {
          const double emin = stod(en.substr(0,idx));
          const double emax = stod(en.substr(idx+1,string::npos));
          if (inRange(sqrtS()/GeV, emin, emax)) {
            _sqs = en;
            break;
          }
        }
        else {
          const double eval = stod(en)*GeV;
          if (isCompatibleWithSqrtS(eval)) {
            _sqs = en; break;
          }
        }
      }
      raiseBeamErrorIf(_sqs.empty());
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const FinalState& fs = apply<FinalState>(event, "FS");
      if (fs.particles().size() != 4) 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<string> _npion;
    string _sqs = "";
    /// @}


  };


  RIVET_DECLARE_PLUGIN(CMD2_2000_I511375);
}