Rivet analyses

title: BESIII_2019_I1743841

Cross section for $K^+K^-K^+K^-$ and $K^+K^-\phi$ for $E_{\text{CMS}}=2.10$ to $3.08$ GeV

Experiment: BESIII (BEPC)

Inspire ID: 1743841

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 1907.06015

Beams: e+ e-

Beam energies: (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (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- to hadrons

Measurement of the cross section for $e^+e^- \to$ $K^+K^-K^+K^-$ and $K^+K^-\phi$ for center of mass energies between 2.10 and 3.08 GeV by the BESIII experiment.

Source code:BESIII_2019_I1743841.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief 2K+2K- and K+K- phi cross section class BESIII_2019_I1743841 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2019_I1743841);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(FinalState(), "FS");
  declare(UnstableParticles(), "UFS");
  // book counters
  for (size_t ix = 0; ix < 2; ++ix) {
    book(_sigma[ix], ix + 1, 1, 1);
  }

  for (const string& en : _sigma[0].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");

  map<long, int> nCount;
  int ntotal(0);
  for (const Particle& p : fs.particles()) {
    nCount[p.pid()] += 1;
    ++ntotal;
  }
  if (ntotal == 4 && nCount[321] == 2 && nCount[-321] == 2) {
    _sigma[0]->fill(_sqs);
  }
  const FinalState& ufs = apply<FinalState>(event, "UFS");
  for (const Particle& p : ufs.particles(Cuts::pid == 333)) {
    if (p.children().empty()) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p, nRes, ncount);
    // phi K+K-
    if (ncount == 2) {
      bool matched = true;
      for (const auto& val : nRes) {
        if (abs(val.first) == 321) {
          if (val.second != 1) {
            matched = false;
            break;
          }
        }
        else if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (matched) {
        _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_2019_I1743841);

} ```