Rivet analyses

Cross section for e+e− → ϕη for energies below 2 GeV

Experiment: CMD3 (VEPP-2M)

Inspire ID: 1740541

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 1906.08006

Beams: e+ e-

Beam energies: ANY

Run details: - e+ e- to hadrons

Measurement of the cross section for e+e− → K+K−η, which is found to be saturated by the resonant ϕη sub-process, and therefore only the cross section for e+e− → ϕη for energies below 2 GeV is extracted by the CMD3 experiment

Source code:CMD3_2019_I1740541.cc

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

namespace Rivet {


  /// @brief phi eta cross section
  class CMD3_2019_I1740541 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CMD3_2019_I1740541);


    /// @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<3; ++ix) {
        book(_c_phi[ix], 1+ix, 1, 6);
        for (const string& en : _c_phi[ix].binning().edges<0>()) {
          const double eval = stod(en)*GeV;
          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;
      }
      const FinalState& ufs = apply<FinalState>(event, "UFS");
      for (const Particle& p : ufs.particles(Cuts::pid==221)) {
        if (p.children().empty()) continue;
        map<long,int> nRes = nCount;
        int ncount = ntotal;
        findChildren(p,nRes,ncount);
        bool matched = false;
        for (const Particle& p2 : ufs.particles(Cuts::pid==333)) {
          map<long,int> nResB = nRes;
          int ncountB = ncount;
          findChildren(p2,nResB,ncountB);
          if (ncountB!=0) continue;
          bool matched = true;
          for (const auto& val : nResB) {
            if (val.second!=0) {
              matched = false;
              break;
            }
          }
          if (matched) {
            for (size_t ix=0; ix<3; ++ix) {
              _c_phi[ix]->fill(_sqs[ix]);
            }
            break;
          }
        }
        if (matched) break;
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _c_phi[3];
    string _sqs[3];
    /// @}


  };


  RIVET_DECLARE_PLUGIN(CMD3_2019_I1740541);
}