Rivet analyses

Cross section for e+e− → ηK+K− for energies below 2 GeV

Experiment: SND (VEPP-2M)

Inspire ID: 1693737

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Atom.Nucl. 81 (2018) no.2, 205-213

Beams: e+ e-

Beam energies: ANY

Run details: - e+ e- to hadrons

Cross section for e+e− → ηK+K− for energies below 2 GeV

Source code:SND_2018_I1693737.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief e+e- > eta K+K-
  class SND_2018_I1693737 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(SND_2018_I1693737);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      book(_nKKEta, "/TMP/nKKEta", refData(1, 1, 1));
    }

    void findChildren(const Particle& p, map<long, int>& nRes, int& ncount) {
      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;
      }
      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 != 2) continue;
        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) {
          _nKKEta->fill(sqrtS());
          break;
        }
      }
    }

    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_nKKEta, crossSection() / sumOfWeights() / nanobarn);
      Estimate1DPtr mult;
      book(mult, 1, 1, 1);
      barchart(_nKKEta, mult);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _nKKEta;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(SND_2018_I1693737);


}