Rivet analyses

title: BESIII_2018_I1704558

Cross section for $e^+e^-\to K^+K^-$ between 2.00 and 3.08 GeV

Experiment: BESIII (BEPC II)

Inspire ID: 1704558

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 1811.08742

Beams: e+ e-

Beam energies: (1.0, 1.0); (1.0, 1.0); (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 between 2.00 and 3.08 GeV

Measurement of the cross section for $e^+e^-\to K^+K^-$ at energies between 2.00 and 3.08 GeV. Useful for comparing models of the kaon form factor.

Source code:BESIII_2018_I1704558.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief Cross section for e+e- -> K+K- between 2.00 and 3.08 GeV class BESIII_2018_I1704558 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1704558);


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

/// Book histograms and initialise projections before the run
void init() {

  // Initialise and register projections
  declare(FinalState(), "FS");

  // Book histograms
  book(_nkaon, 1, 1, 1);
  for (const string& en : _nkaon.binning().edges<0>()) {
    const double eval = stod(en);
    if (isCompatibleWithSqrtS(eval)) {
      _sqs = en;
      break;
    }
  }
  raiseBeamErrorIf(_sqs.empty());
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  const FinalState& fs = apply<FinalState>(event, "FS");
  if (fs.particles().size() != 2) vetoEvent;
  for (const Particle& p : fs.particles()) {
    if (p.abspid() != PID::KPLUS) vetoEvent;
  }
  _nkaon->fill(_sqs);
}


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

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _nkaon;
string _sqs = "";
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2018_I1704558);

} ```