Rivet analyses

title: BESIII_2023_I2686032

Cross section for $e^+e^-\to\Lambda^0\bar{\Sigma}^0+\text{c.c.}$ 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 $e^+e^-\to\Lambda^0\bar{\Sigma}^0+\text{c.c.}$ for $\sqrt{s}=2.3094\to3.0800\,$GeV by the BESIII collaboration.

Source code:BESIII_2023_I2686032.cc

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

} ```