Rivet analyses

Cross section for e+e− → ηJ/ψ for energies between 3.81 and 4.60 GeV

Experiment: BESIII (BEPC)

Inspire ID: 1784442

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 102 (2020) 3, 031101

Beams: e+ e-

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

Run details: - e+ e- to hadrons

Cross section for e+e− → ηJ/ψ for energies between 3.81 and 4.60 GeV measured by the BESIII collaboration.

Source code:BESIII_2020_I1784442.cc

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

namespace Rivet {


  /// @brief e+e- -> eta J/psi
  class BESIII_2020_I1784442 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1784442);


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

    /// Book histograms and initialise projections before the run
    void init() {
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      for (size_t ix = 0; ix < 2; ++ix) {
        book(_sigmaJPsi[ix], 1 + ix, 1, 1);
        for (const string& en : _sigmaJPsi[ix].binning().edges<0>()) {
          const double eval = stod(en) * GeV;
          if (isCompatibleWithSqrtS(eval)) {
            _sqs[ix] = en;
            break;
          }
        }
      }
      raiseBeamErrorIf(_sqs[0].empty() && _sqs[1].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 == PID::JPSI)) {
        if (p.children().empty()) continue;
        // find the J/psi
        map<long, int> nRes = nCount;
        int ncount = ntotal;
        findChildren(p, nRes, ncount);
        bool matched = false;
        for (const Particle& p2 : ufs.particles(Cuts::pid == PID::ETA)) {
          if (p2.children().empty()) continue;
          bool JpsiParent = false;
          Particle parent = p2;
          while (!parent.parents().empty()) {
            parent = parent.parents()[0];
            if (parent.pid() == PID::JPSI) {
              JpsiParent = true;
              break;
            }
          }
          if (JpsiParent) continue;
          map<long, int> nRes2 = nRes;
          int ncount2 = ncount;
          findChildren(p2, nRes2, ncount2);
          if (ncount2 != 0) continue;
          matched = true;
          for (const auto& val : nRes2) {
            if (val.second != 0) {
              matched = false;
              break;
            }
          }
          if (matched) {
            for (unsigned int ix = 0; ix < 2; ++ix)
              if (!_sqs[ix].empty()) {
                _sigmaJPsi[ix]->fill(_sqs[ix]);
                break;
              }
          }
        }
        if (matched) break;
      }
    }


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

    /// @}


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


  RIVET_DECLARE_PLUGIN(BESIII_2020_I1784442);

}