Rivet analyses

Cross section for e+e− → ηhc for energies between 4.1 and 4.6 GeV

Experiment: BESIII (BEPC)

Inspire ID: 2775801

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 111 (2025) 1, L011101 - arXiv: 2404.06718

Beams: e+ e-

Beam energies: (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); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3)GeV

Run details: - e+ e- to hadrons.

Cross section for e+e− → ηhc for energies between 4.1 and 4.6 GeV measured by the BESIII collaboration.

Source code:BESIII_2024_I2775801.cc

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

namespace Rivet {


  /// @brief e+ e- > eta h_c
  class BESIII_2024_I2775801 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2024_I2775801);


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

    /// Book histograms and initialise projections before the run
    void init() {
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      book(_nhc, 1, 1, 1);
      for (const string& en : _nhc.binning().edges<0>()) {
        const double eval = stod(en) * MeV;
        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()];
          --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");
      // loop over h_c
      for (const Particle& hc : ufs.particles(Cuts::pid == 10443)) {
        if (hc.children().empty()) continue;
        map<long, int> nRes = nCount;
        int ncount = ntotal;
        findChildren(hc, nRes, ncount);
        bool matched = false;
        // loop over eta
        for (const Particle& eta : ufs.particles(Cuts::pid == 221)) {
          // check eta not child of h_c
          Particle parent = eta;
          while (!parent.parents().empty()) {
            parent = parent.parents()[0];
            if (parent.abspid() == 10443) break;
          }
          if (fuzzyEquals(parent.mom(), hc.mom())) continue;
          map<long, int> nRes2 = nRes;
          int ncount2 = ncount;
          findChildren(eta, nRes2, ncount2);
          if (ncount2 != 0) continue;
          matched = true;
          for (const auto& val : nRes2) {
            if (val.second != 0) {
              matched = false;
              break;
            }
          }
          if (matched) {
            _nhc->fill(_sqs);
            break;
          }
        }
        if (matched) break;
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _nhc;
    string _sqs = "";
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2024_I2775801);
}