Rivet analyses

title: BESIII_2018_I1699641

Cross section for $e^+e^-\to K^0_SK^\pm\pi^\mp\pi^0$ and $K^0_SK^\pm\pi^\mp\eta$ between 3.90 to 4.60 GeV

Experiment: BESIII (BEPC II)

Inspire ID: 1699641

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 1810.09395

Beams: e+ e-

Beam energies: (1.9, 1.9); (2.0, 2.0); (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); (2.2, 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)GeV

Run details: - e+e- to hadrons

Measurement of the cross section for $e^+e^-\to K^0_SK^\pm\pi^\mp\pi^0$ and $K^0_SK^\pm\pi^\mp\eta$ between 3.90 to 4.60 GeV.

Source code:BESIII_2018_I1699641.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Cross section for e+e- K0SK+-\pi+-\pi0 and K0SK+-pi-+eta between 3.90 to 4.60 GeV class BESIII_2018_I1699641 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1699641);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(FinalState(), "FS");
  declare(UnstableParticles(), "UFS");

  // Book histograms
  for (size_t ix = 0; ix < 2; ++ix) {
    book(_sigma[ix], 1 + ix, 1, 1);
  }

  for (const string& en : _sigma[0].binning().edges<0>()) {
    const double eval = stod(en) * GeV;
    if (isCompatibleWithSqrtS(eval)) {
      _sqs = en;
      break;
    }
  }
  if (_sqs.empty() && isCompatibleWithSqrtS(4.085))
    _sqs = "4.085"s;
  else
    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");

  map<long, int> nCount;
  int ntotal(0);
  for (const Particle& p : fs.particles()) {
    nCount[p.pid()] += 1;
    ++ntotal;
  }
  // K K pi pi
  if (ntotal == 4 && nCount[310] == 1 && nCount[111] == 1
      && ((nCount[321] == 1 && nCount[-211] == 1) || (nCount[-321] == 1 && nCount[211] == 1))) {
    _sigma[0]->fill(_sqs);
  }
  // eta resonance
  const FinalState& ufs = apply<FinalState>(event, "UFS");
  for (const Particle& p : ufs.particles()) {
    if (p.children().empty()) continue;
    if (p.pid() != 221) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p, nRes, ncount);
    if (ncount != 3) continue;
    bool matched = true;
    for (const auto& val : nRes) {
      if (abs(val.first) == 321 || abs(val.first) == 211) {
        continue;
      }
      else if (abs(val.first) == 310) {
        if (val.second != 1) {
          matched = false;
          break;
        }
      }
      else if (val.second != 0) {
        matched = false;
        break;
      }
    }
    if (matched == false) continue;
    if ((nCount[321] == 1 && nCount[-211] == 1) || (nCount[-321] == 1 && nCount[211] == 1)) {
      _sigma[1]->fill(_sqs);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_sigma, crossSection() / sumOfWeights() / picobarn);
}
/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _sigma[2];
string _sqs = "";
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2018_I1699641);

} ```