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(auto const & 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);


}