Rivet analyses

Cross Section for e+e− → K+K−π0 and ϕπ0 from threshold to 2.1 GeV

Experiment: SND (VEPP-2000)

Inspire ID: 1806118

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 2006.05465

Beams: e+ e-

Beam energies: ANY

Run details: - e+ e- to hadrons

Cross section for e+e− → K+K−π0 between threshold and 2.1 GeV. The ϕπ0 radiative subprocess is also measured.

Source code:SND_2020_I1806118.cc

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

namespace Rivet {


  /// @brief e+e- -> K+K-pi0
  class SND_2020_I1806118 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(SND_2020_I1806118);


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

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

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

      // Book histograms
      book(_nKKPi, 1, 1, 1);
      book(_nPhiPi, "TMP/nPhiPi", refData(2, 1, 1));
      for (const string& en : _nKKPi.binning().edges<0>()) {
        double end = stod(en) * GeV;
        if (isCompatibleWithSqrtS(end, 5e-3)) {
          _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 == 3 && nCount[321] == 1 && nCount[-321] == 1 && nCount[111] == 1) {
        // KK pi state
        _nKKPi->fill(_sqs);
      }
      // phi pi state
      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);
        if (ncount != 1) continue;
        bool matched = true;
        for (const auto& val : nRes) {
          if (val.first == 111) {
            if (val.second != 1) {
              matched = false;
              break;
            }
          }
          else if (val.second != 0) {
            matched = false;
            break;
          }
        }
        if (matched) {
          _nPhiPi->fill(sqrtS() / GeV);
          break;
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      double fact = crossSection() / sumOfWeights() / nanobarn;
      scale(_nKKPi, fact);
      scale(_nPhiPi, fact);
      Estimate1DPtr mult;
      book(mult, 2, 1, 1);
      barchart(_nPhiPi, mult);
    }
    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _nKKPi;
    Histo1DPtr _nPhiPi;
    string _sqs = "";
    /// @}
  };


  RIVET_DECLARE_PLUGIN(SND_2020_I1806118);
}