Rivet analyses

Cross section for e+e− → Ω−Ω̄+ for $\sqrt{s}=3.7\to4.7\,$GeV

Experiment: BESIII (BEPC)

Inspire ID: 2957171

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2508.01359

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); (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); (2.3, 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- -> hadrons

Measurement of the cross section for e+e− → Ω−Ω̄+ for $\sqrt{s}=3.7\to4.7\,$GeV by the BESIII collaboration.

Source code:BESIII_2025_I2957171.cc

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


  /// @brief e+e- > Omega+ Omega-
  class BESIII_2025_I2957171 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2025_I2957171);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(Cuts::abspid==3334), "UFS");
      book(_sigma, 1,1,1);

      for (const string& en : _sigma.binning().edges<0>()) {
        double end = std::stod(en)*GeV;
        if (isCompatibleWithSqrtS(end)) {
          _ecms = en;
          break;
        }
      }
      raiseBeamErrorIf(_ecms.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");
      // total hadronic and muonic cross sections
      map<long,int> nCount;
      int ntotal(0);
      for (const Particle& p : fs.particles()) {
        nCount[p.pid()] += 1;
        ++ntotal;
      }

      // find the Lambdas and Sigmas
      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& p1 : ufs.particles()) {
        bool matched = false;
        // check fs
        bool fs = true;
        for (const Particle& child : p1.children()) {
          if (child.pid()==p1.pid()) {
            fs = false;
            break;
          }
        }
        if (!fs) continue;
        // find the children
        map<long,int> nRes = nCount;
        int ncount = ntotal;
        findChildren(p1,nRes,ncount);
        for (const Particle & p2 : ufs.particles(Cuts::pid==-p1.pid())) {
          // check fs
          bool fs = true;
          for (const Particle& child : p2.children()) {
            if (child.pid()==p2.pid()) {
              fs = false;
              break;
            }
          }
          if (!fs) 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) {
            _sigma->fill(_ecms);
            break;
          }
        }
        if (matched) break;
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      double fact  = crossSection()/ sumOfWeights() /femtobarn;
      scale(_sigma, fact);
      double mOmega = 1.67244;
      double tau  = 0.25*sqr(sqrtS()/mOmega);
      double beta = sqrt(1.-1./tau);
      double alpha = 7.2973525693e-3;
      double GeV2fb = 0.3893793721e12;
      double sigma0 = 4.*M_PI*sqr(alpha/sqrtS())*beta*GeV2fb/3.;
      BinnedEstimatePtr<string> tmp;
      book(tmp,1,1,2);
      for (const auto& b :_sigma->bins()) {
        tmp->bin(b.index()).set(1e3*sqrt(b.sumW()/(sigma0*(1. + 0.5/tau))),
                               1e3*0.5*sqrt(1./b.sumW()/sigma0/(1. + 0.5/tau))*b.errW());
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _sigma;
    string _ecms;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BESIII_2025_I2957171);

}