Rivet analyses

Cross section for e+e− → ωπ0 → π0π0γ at energies near the ϕ mass.’

Experiment: SND (VEPP-2M)

Inspire ID: 503946

Status: VALIDATED

Authors: - Peter Richardson

References: - Nucl. Phys (2000) B569, 158-182

Beams: e+ e-

Beam energies: (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5)GeV

Run details: - e+e- to hadrons

Measurement of the cross section for e+e− → ωπ0 → π0π0γ at energies near the ϕ mass.

Source code:SND_2000_I503946.cc

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


namespace Rivet {


  /// @brief e+e- -> omega pi0
  class SND_2000_I503946 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(SND_2000_I503946);


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

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

      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      book(_numOmegaPi, 1, 1, 1);
      for (const string& en : _numOmegaPi.binning().edges<0>()) {
        double eval = stod(en) * MeV;
        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;
      }
      // three particles (pi0 pi0 gamma)
      if (ntotal != 3) vetoEvent;
      const FinalState& ufs = apply<FinalState>(event, "UFS");
      for (const Particle& p : ufs.particles()) {
        if (p.children().empty()) continue;
        // find the omega
        if (p.pid() == 223) {
          map<long, int> nRes;
          int ncount(0);
          findChildren(p, nRes, ncount);
          // only omega to pi0 gamma mode
          if (ncount != 2) continue;
          if (nRes[111] != 1 || nRes[22] != 1) continue;
          // omega pi0
          if (nCount[111] - nRes[111] == 1) _numOmegaPi->fill(_sqs);
        }
      }
    }


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

    /// @}


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


  RIVET_DECLARE_PLUGIN(SND_2000_I503946);
}