Rivet analyses

Cross section for e+e− → Ξ−Ξ̄+ for $\sqrt{s}=3.510\to4.843\,$GeV

Experiment: BESIII (BEPC)

Inspire ID: 2695411

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2309.04215

Beams: e+ e-

Beam energies: (1.8, 1.8); (1.8, 1.8); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (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); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.4, 2.4); (2.4, 2.4)GeV

Run details: - e+ e- -> hadrons

Measurement of the cross section for e+e− → Ξ−Ξ̄+ for $\sqrt{s}=3.510\to4.843\,$GeV by the BESIII collaboration.

Source code:BESIII_2023_I2695411.cc

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

namespace Rivet {


  /// @brief  e+e- > Xi+ Xi-
  class BESIII_2023_I2695411 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2023_I2695411);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(Cuts::abspid == 3312), "UFS");
      book(_sigmaXi, 1, 1, 1);
      for (const string& en : _sigmaXi.binning().edges<0>()) {
        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");
      // 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) {
            _sigmaXi->fill(_sqs);
            break;
          }
        }
        if (matched) break;
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      double mXi = 1.32171;
      double alpha = 7.2973525693e-3;
      double GeV2fb = 0.3893793721e12;
      scale(_sigmaXi, crossSection() / sumOfWeights() / femtobarn);
      BinnedEstimatePtr<string> tmp;
      book(tmp, 1, 1, 2);
      for (const auto& b : _sigmaXi->bins()) {
        double eval = stod(b.xEdge());
        double tau = 0.25 * sqr(eval / mXi);
        double beta = sqrt(1. - 1. / tau);
        double sigma0 = 4. * M_PI * sqr(alpha / eval) * beta * GeV2fb / 3.;
        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> _sigmaXi;
    string _sqs = "";
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2023_I2695411);

}