Rivet analyses

Cross section for K+K−K+K− and K+K−ϕ for ECMS = 2.10 to 3.08 GeV

Experiment: BESIII (BEPC)

Inspire ID: 1743841

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 1907.06015

Beams: e+ e-

Beam energies: (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.2, 1.2); (1.2, 1.2); (1.2, 1.2); (1.2, 1.2); (1.3, 1.3); (1.3, 1.3); (1.4, 1.4); (1.4, 1.4); (1.4, 1.4); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5)GeV

Run details: - e+e- to hadrons

Measurement of the cross section for e+e−→ K+K−K+K− and K+K−ϕ for center of mass energies between 2.10 and 3.08 GeV by the BESIII experiment.

Source code:BESIII_2019_I1743841.cc

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

namespace Rivet {


  /// @brief 2K+2K- and K+K- phi cross section
  class BESIII_2019_I1743841 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2019_I1743841);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      // book counters
      for (size_t ix=0; ix<2; ++ix) {
        book(_sigma[ix], ix+1, 1, 1);
      }

      for (const string& en : _sigma[0].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;
      }
      if (ntotal==4 && nCount[321]==2 && nCount[-321]==2) {
        _sigma[0]->fill(_sqs);
      }
      const FinalState& ufs = apply<FinalState>(event, "UFS");
      for (const Particle& p :  ufs.particles(Cuts::pid==333)) {
        if (p.children().empty()) continue;
        map<long,int> nRes=nCount;
        int ncount = ntotal;
        findChildren(p,nRes,ncount);
        // phi K+K-
        if (ncount==2) {
          bool matched = true;
          for (const auto& val : nRes) {
            if (abs(val.first)==321) {
              if (val.second!=1) {
                matched = false;
                break;
              }
            }
            else if (val.second!=0) {
              matched = false;
              break;
            }
          }
          if (matched) {
            _sigma[1]->fill(_sqs);
          }
        }
      }
    }


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

    /// @}


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

  };


  RIVET_DECLARE_PLUGIN(BESIII_2019_I1743841);

}