Rivet analyses

Cross section for e+e− → πγ and ηγ for energies between 600 MeV and 1380 MeV

Experiment: CMD2 (VEPP-2M)

Inspire ID: 658856

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett. B605 (2005) 26-36

Beams: e+ e-

Beam energies: (0.3, 0.3); (0.3, 0.3); (0.3, 0.3); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.6, 0.6); (0.7, 0.7)GeV

Run details: - e+ e- to hadrons below 0.6 and 1.38 GeV

Cross section for e+e− → πγ and ηγ for energies between 600 MeV and 1380 MeV.

Source code:CMD2_2005_I658856.cc

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

namespace Rivet {


  /// @brief e+e- > eta or pi0  + gamma
  class CMD2_2005_I658856 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CMD2_2005_I658856);


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

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

      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      for (size_t ix=0; ix<2; ++ix) {
        book(_sigma[ix], 1+ix, 1, 1);
        for (const string& en : _sigma[ix].binning().edges<0>()) {
          const double eval = stod(en)*MeV;
          if (isCompatibleWithSqrtS(eval)) {
            _sqs[ix] = en; break;
          }
        }
      }
      raiseBeamErrorIf(_sqs[0].empty() && _sqs[1].empty() && _sqs[2].empty());
    }

    void findChildren(const Particle& p, map<long,int>& nRes, int& ncount) const {
      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) {

      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) _sigma[1]->fill(_sqs[1]);


      const FinalState& ufs = apply<FinalState>(event, "UFS");
      for (const Particle& p : ufs.particles()) {
        if (p.children().empty()) continue;
        // find the omega
        if (p.pid()==221) {
          map<long,int> nRes = nCount;
          int ncount = ntotal;
          findChildren(p,nRes,ncount);
          // eta pi+pi-
          if (ncount!=1) continue;
          bool matched = true;
          for (const auto& val : nRes) {
            if (val.first==22) {
              if (val.second !=1) {
                matched = false;
                break;
              }
            }
            else if (val.second!=0) {
              matched = false;
              break;
            }
          }
          if (matched) _sigma[0]->fill(_sqs[0]);
        }
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _sigma[2];
    string _sqs[2];
    /// @}


  };


  RIVET_DECLARE_PLUGIN(CMD2_2005_I658856);
}