Rivet analyses

Cross section for e+e− → DD̄ near the ψ(3770) resonance

Experiment: BESIII (BEPC)

Inspire ID: 1794583

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 109 (2024) 11, 114010 - arXiv: 2404.03896 - URN/HDL:11299/199064

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); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9)GeV

Run details: - e+ e- > hadrons

Measurement of the cross section for e+e− → DD̄ near the ψ(3770) resonance. The experimental values are taken from PhD thesis of A. Julin together with the extraction of the Born cross section from Phys.Rev.D 109 (2024) 11, 114010.

Source code:BESIII_2017_I1794583.cc

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

namespace Rivet {


  /// @brief  e+e- -> D Dbar
  class BESIII_2017_I1794583 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2017_I1794583);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(Cuts::abspid==411 || Cuts::abspid==421), "UFS");
      book(_sigma[0], 1, 1, 1);
      book(_sigma[1], 2, 1, 1);

      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()]-=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 (size_t ix=0; ix<ufs.particles().size(); ++ix) {
        const Particle& p1 = ufs.particles()[ix];
        map<long,int> nRes = nCount;
        int ncount = ntotal;
        findChildren(p1,nRes,ncount);
        bool matched=false;
        for (size_t iy=ix+1; iy<ufs.particles().size(); ++iy) {
          const Particle& p2 = ufs.particles()[iy];
          if (p2.pid() != -p1.pid()) continue;
          if (!p2.parents().empty() && p2.parents()[0].pid()==p1.pid()) 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) break;
        }
        if (matched) {
          _sigma[int(p1.abspid()!=421)]->fill(_sqs);
          break;
        }
      }
    }


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

    /// @}


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


  };


  RIVET_DECLARE_PLUGIN(BESIII_2017_I1794583);
}