Rivet analyses

Cross section for e+e− → Λ0Σ̄0 + c.c. for $\sqrt{s}=2.3094\to3.0800\,$GeV

Experiment: BESIII (BEPC)

Inspire ID: 2686032

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2308.03361

Beams: e+ e-

Beam energies: (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- -> hadrons

Measurement of the cross section for e+e− → Λ0Σ̄0 + c.c. for $\sqrt{s}=2.3094\to3.0800\,$GeV by the BESIII collaboration.

Source code:BESIII_2023_I2686032.cc

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

namespace Rivet {


  /// @brief e+e- > Lambda0 Sigmabar0 + c.c.
  class BESIII_2023_I2686032 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2023_I2686032);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      book(_nLS, 1, 1, 1);
      for (const string& en : _nLS.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");
      // 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(Cuts::abspid == 3122)) {
        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);
        int sign = p1.pid() / 3122;
        for (const Particle& p2 : ufs.particles(Cuts::pid == -sign * 3212)) {
          // 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) {
            _nLS->fill(_sqs);
            break;
          }
        }
        if (matched) break;
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_nLS, crossSection() / sumOfWeights() / picobarn);
      const double mL = 1.115683;
      const double mS = 1.192642;
      const double alpha = 7.2973525693e-3;
      const double GeV2pb = 0.3893793721e9;
      BinnedEstimatePtr<string> tmp;
      book(tmp, 1, 1, 2);
      for (const auto& b : _nLS->bins()) {
        const double eval = std::stod(b.xEdge());
        const double tau = sqr(eval / (mL + mS));
        const double beta = sqrt(1. - 2. * (sqr(mS) + sqr(mL)) / sqr(sqrtS())
                                 + sqr((sqr(mS) - sqr(mL)) / sqr(eval)));
        const double sigma0 = 4. * M_PI * sqr(alpha / eval) * beta * GeV2pb;
        tmp->bin(b.index()).set(sqrt(3. * b.sumW() * tau / (sigma0 * (0.5 + 0.5 * tau))),
                                sqrt(1.5 * tau / b.sumW() / sigma0 / (1. + 2. * tau)) * b.errW());
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _nLS;
    string _sqs = "";
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2023_I2686032);

}