Rivet analyses

Cross section for e+e− → pp̄η and pp̄ω at energies between 3.773 and 4.600 GeV

Experiment: BESIII (BEPC)

Inspire ID: 1845443

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 104 (2021) 9, 092008

Beams: e+ e-

Beam energies: (1.9, 1.9); (1.9, 1.9); (2.0, 2.0); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.2, 2.2); (2.2, 2.2); (2.3, 2.3)GeV

Run details: - e+e- to hadrons

Cross section for e+e− → pp̄η and pp̄ω at energies between 3.773 and 4.600 GeV measured by the BESIII collaboration.

Source code:BESIII_2021_I1845443.cc

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

namespace Rivet {


  /// @brief  e+e- -> p pbar eta/omega
  class BESIII_2021_I1845443 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1845443);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      book(_nEta,   1,1,1);
      book(_nOmega, 2,1,1);
      for (const string& en : _nOmega.binning().edges<0>()) {
        const double eval = stod(en);
        if (isCompatibleWithSqrtS(eval)) {
          _sqs = en; break;
        }
      }
      raiseBeamErrorIf(_sqs.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()]-=1;
          --ncount;
        }
        else {
          findChildren(child,nRes,ncount);
        }
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const FinalState& fs = apply<FinalState>(event, "FS");
      // total hadronic and muonic cross sections
      map<long,int> nCount;
      int ntotal(0);
      for (const Particle& p : fs.particles()) {
        nCount[p.pid()] += 1;
        ++ntotal;
      }
      // find the eta/omega
      const FinalState& ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& p : ufs.particles(Cuts::pid==PID::ETA or Cuts::pid==PID::OMEGA)) {
        map<long,int> nRes = nCount;
        int ncount = ntotal;
        findChildren(p,nRes,ncount);
        bool matched=true;
        for (const auto& val : nRes) {
          if (abs(val.first)==PID::PROTON) {
            if (val.second!=1) {
              matched = false;
              break;
            }
          }
          else if (val.second!=0) {
            matched = false;
            break;
          }
        }
        if (matched) {
          if (p.pid()==PID::ETA) {
            _nEta->fill(_sqs);
          }
          else {
            _nOmega->fill(_sqs);
          }
          break;
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      const double fact = crossSection()/ sumOfWeights() /picobarn;
      scale(_nEta  ,fact);
      scale(_nOmega,fact);
    }

    ///@}


    /// @name Histograms
    ///@{
    BinnedHistoPtr<string> _nEta,_nOmega;
    string _sqs = "";
    ///@}


  };


  RIVET_DECLARE_PLUGIN(BESIII_2021_I1845443);

}