Rivet analyses

Cross section for e+e− → 3(π+π−) below 2 GeV by CMD3

Experiment: CMD3 (VEPP-2M)

Inspire ID: 1217420

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 1302.0053

Beams: e+ e-

Beam energies: ANY

Run details: - e+ e- to hadrons

Measurement of the cross section for e+e− → 3(π+π−) for energies below 2 GeV by the CMD3 experiment

Source code:CMD3_2013_I1217420.cc

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

namespace Rivet {


  /// @brief e+e- -> 3(pi+pi-)
  class CMD3_2013_I1217420 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CMD3_2013_I1217420);


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

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

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

      // Book histograms
      for (unsigned int ix = 0; ix < 3; ++ix) book(_sigma[ix], 1, 1, 1 + ix);
    }

    void findChildren(const Particle& p, map<long, int>& nRes, int& ncount) {
      for (const Particle& child : p.children()) {
        if (child.children().empty()) {
          --nRes[child.pid()];
          --ncount;
        }
        else
          findChildren(child, nRes, ncount);
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // find the final-state particles
      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 == 6 && nCount[211] == 3 && nCount[-211] == 3) {
        for (unsigned int ix = 0; ix < 3; ++ix) _sigma[ix]->fill(round(sqrtS() / MeV));
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      double fact = crossSection() / nanobarn / sumOfWeights();
      for (unsigned int ix = 0; ix < 3; ++ix) scale(_sigma[ix], fact);
    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<int> _sigma[3];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(CMD3_2013_I1217420);


}