Rivet analyses

Cross section for e⁺e⁻ → π⁺π⁻X(3823)( → γχ_c1) and π⁺π⁻ψ(2S) for $\sqrt{s}=4.23$ to 4.6 GeV

Experiment: BESIII (BEPC)

Inspire ID: 1356733

Status: VALIDATED NOHEPDATA SINGLEWEIGHT

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 115 (2015) 1, 011803

Beams: e+ e-

Beam energies: (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, pi0 set stable

Measurement of the cross section for e⁺e⁻ → π⁺π⁻X(3823)( → γχ_c1) and π⁺π⁻ψ(2S) for $\sqrt{s}=4.23$ to 4.6 GeV. The X(3823) is consistent with the ψ(1³D₂) state and therefore we use the PDG code 20445, although this can be changed using the PID option.

Source code:`BESIII_2015_I1356733.cc`

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

namespace Rivet {


  /// @brief e+e- to hadrons
  class BESIII_2015_I1356733 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2015_I1356733);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // set the PDG code
      _pid = getOption<double>("PID", 20445);
      // projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(Cuts::pid== 20443 || Cuts::pid==100443), "UFS");
      // histograms
      for (size_t ix=0; ix<2; ++ix) {
        book(_sigma[ix], 1, 1, 1+ix);
      }

      for (const string& en : _sigma[0].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;
      }
      for (const Particle& psi : apply<UnstableParticles>(event, "UFS").particles()) {
        if (psi.children().empty()) continue;
        map<long,int> nRes = nCount;
        int ncount = ntotal;
        findChildren(psi,nRes,ncount);
        int nphoton = psi.pid()==100443 ? 0 : 1;
        if (ncount!=2+nphoton) continue;
        bool matched = true;
        for (const auto& val : nRes) {
          if (abs(val.first)==211) {
            if (val.second !=1) {
              matched = false;
              break;
            }
          }
          else if (val.first==22) {
            if (val.second!=nphoton) {
              matched = false;
              break;
            }
          }
          else if (val.second!=0) {
            matched = false;
            break;
          }
        }
        if (matched) {
          if (nphoton==0) {
            _sigma[1]->fill(_sqs);
            break;
          }
          else {
            Particle parent = psi.parents()[0];
            if (parent.pid()==_pid && parent.children().size()==2 &&
               (parent.children()[0].pid()==22 || parent.children()[1].pid()==22 )) {
              _sigma[0]->fill(_sqs);
              break;
            }
          }
        }
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _sigma[2];
    string _sqs = "";
    int _pid;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BESIII_2015_I1356733);

}

Rivet analyses

Cross section for e+e− → π+π−X(3823)( → γχc1) and π+π−ψ(2S) for $\sqrt{s}=4.23$ to 4.6 GeV

Source code:BESIII_2015_I1356733.cc

Cross section for e⁺e⁻ → π⁺π⁻X(3823)( → γχ_c1) and π⁺π⁻ψ(2S) for $\sqrt{s}=4.23$ to 4.6 GeV

Source code:`BESIII_2015_I1356733.cc`