Rivet analyses

Cross section for e+e− → π+π−π0ηc between 4.18 and 4.60 GeV

Experiment: BESIII (BEPC)

Inspire ID: 1826422

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 103 (2021) 3, 032006

Beams: e+ e-

Beam energies: (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, KS0 and pi0 should be set stable

Cross section for e+e− → π+π−π0ηc between 4.18 and 4.60 GeV

Source code:BESIII_2021_I1826422.cc

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

namespace Rivet {


  /// @brief e+e- -> pi+ pi- pi0 eta_c
  class BESIII_2021_I1826422 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1826422);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      book(_sigma, 1,1,1);
      for (const string& en : _sigma.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");
      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& chi : ufs.particles(Cuts::pid==445)) {
        if (chi.children().empty()) continue;
        map<long,int> nRes=nCount;
        int ncount = ntotal;
        findChildren(chi,nRes,ncount);
        if (ncount!=3) continue;
        bool matched = true;
        for (const auto& val : nRes) {
          if (abs(val.first)==211 || val.first==111) {
            if (val.second!=1) {
              matched = false;
              break;
            }
          }
          else if (val.second!=0) {
            matched = false;
            break;
          }
        }
        if (matched) {
          _sigma->fill(_sqs);
          break;
        }
      }
    }


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

    /// @}


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


  };


  RIVET_DECLARE_PLUGIN(BESIII_2021_I1826422);

}