Rivet analyses

Cross section for e⁺e⁻ → ψ(2S)π⁺π⁻ at energies between 4.0 and 4.7 GeV

Experiment: BESIII (BEPC)

Inspire ID: 1933191

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.D 104 (2021) 5, 052012

Beams: e+ e-

Beam energies: (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); (2.2, 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)GeV

Run details: - e+e- to hadrons

Measurement of the cross section for e⁺e⁻ → ψ(2S)π⁺π⁻ at energies between 4.0 and 4.7 GeV by the BES collaboration.

Source code:`BESIII_2021_I1933191.cc`

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

namespace Rivet {


  /// @brief e+e- > psi(2S) pi+pi-
  class BESIII_2021_I1933191 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1933191);


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

    /// Book histograms and initialise projections before the run
    void init() {
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      book(_nPsi2s, 1, 1, 3);
      for (const string& en : _nPsi2s.binning().edges<0>()) {
        const double eval = stod(en)*GeV;
        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");
      for (const Particle& p : ufs.particles()) {
        if (p.children().empty()) continue;
        // find the psi(2S)
        if (p.pid()==100443) {
          map<long,int> nRes = nCount;
          int ncount = ntotal;
          findChildren(p,nRes,ncount);
          // omega pi+pi-
          if (ncount!=2) continue;
          bool matched = true;
          for (const auto& val : nRes) {
            if (abs(val.first)==211) {
              if (val.second !=1) {
                matched = false;
                break;
              }
            }
            else if (val.second!=0) {
              matched = false;
              break;
            }
          }
          if (matched) {
            _nPsi2s->fill(_sqs);
            break;
          }
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_nPsi2s, crossSection()/ sumOfWeights() /picobarn);
    }

    ///@}


    /// @name Histograms
    ///@{
    BinnedHistoPtr<string> _nPsi2s;
    string _sqs = "";
    ///@}


  };


  RIVET_DECLARE_PLUGIN(BESIII_2021_I1933191);

}

Rivet analyses

Cross section for e+e− → ψ(2S)π+π− at energies between 4.0 and 4.7 GeV

Source code:BESIII_2021_I1933191.cc

Cross section for e⁺e⁻ → ψ(2S)π⁺π⁻ at energies between 4.0 and 4.7 GeV

Source code:`BESIII_2021_I1933191.cc`