Rivet analyses

title: BESIII_2018_I1681638

$e^+e^-\to pK^0_S\bar{n}K^-$+c.c. between 3.773 and 4.6 GeV

Experiment: BESIII (BEPC)

Inspire ID: 1681638

Status: VALIDATED NOHEPDATA

Authors: - Peter Richrdson

References: - Phys.Rev.D 98 (2018) 3, 032014

Beams: e+ e-

Beam energies: (1.9, 1.9); (2.0, 2.0); (2.1, 2.1); (2.1, 2.1); (2.2, 2.2); (2.2, 2.2); (2.3, 2.3)GeV

Run details: - e+ e- to hadrons

Measurement of the cross section for $e^+e^-\to pK^0_S\bar{n}K^-$+c.c., and the resonant sub-processes $\Lambda(1520)^0\bar{n}K^0_S$+c.c. and $\Lambda(1520)^0\bar{p}K^+$+c.c., for energies between 1.6 and 2 GeV by the BESIII experiment.

Source code:BESIII_2018_I1681638.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+e- -> p KS0 nbar K- class BESIII_2018_I1681638 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1681638);


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

/// Book histograms and initialise projections before the run
void init() {
  declare(FinalState(), "FS");
  declare(UnstableParticles(Cuts::pid == 102134), "UFS");
  // counters
  for (size_t ix = 0; ix < 3; ++ix) {
    book(_sigma[ix], 1, 1, 1 + ix);
  }

  for (const string& en : _sigma[0].binning().edges<0>()) {
    const double eval = stod(en) * GeV;
    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()];
      --ncount;
    }
    else {
      findChildren(child, nRes, ncount);
    }
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  // find the final-state particles
  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;
  }
  // FS
  if (ntotal == 4 && nCount[310] == 1) {
    if ((nCount[2212] == 1 && nCount[-2112] == 1 && nCount[-321] == 1)
        || (nCount[-2212] == 1 && nCount[2112] == 1 && nCount[321] == 1)) {
      _sigma[0]->fill(_sqs);
    }
  }
  for (const Particle& p : apply<FinalState>(event, "UFS").particles()) {
    if (p.children().empty()) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p, nRes, ncount);
    if (ncount != 2) continue;
    bool matched = true;
    int sign = p.pid() / p.abspid();
    for (const auto& val : nRes) {
      if (val.first == -sign * 2112 || val.first == 310) {
        if (val.second != 1) {
          matched = false;
          break;
        }
      }
      else if (val.second != 0) {
        matched = false;
        break;
      }
    }
    if (matched) {
      _sigma[1]->fill(_sqs);
      break;
    }
    matched = true;
    for (const auto& val : nRes) {
      if (val.first == -sign * 2212 || val.first == sign * 321) {
        if (val.second != 1) {
          matched = false;
          break;
        }
      }
      else if (val.second != 0) {
        matched = false;
        break;
      }
    }
    if (matched) {
      _sigma[2]->fill(_sqs);
      break;
    }
  }
}


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

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _sigma[3];
string _sqs = "";
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2018_I1681638);

} ```