Rivet analyses

title: BESIII_2025_I2957171

Cross section for $e^+e^-\to\Omega^-\bar{\Omega}^+$ 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 $e^+e^-\to\Omega^-\bar{\Omega}^+$ for $\sqrt{s}=3.7\to4.7\,$GeV by the BESIII collaboration.

Source code:BESIII_2025_I2957171.cc

```c++ // -- 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);

} ```