Rivet analyses

Cross section for e+e− → ωπ0 → π0π0γ between 0.92 and 1.38 GeV

Experiment: CMD2 (VEPP-2M)

Inspire ID: 616446

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett. B562 (2003) 173-181, 2003

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); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.7, 0.7); (0.7, 0.7); (0.7, 0.7); (0.7, 0.7); (0.7, 0.7)GeV

Run details: - e+e- to hadrons

Measurement of the cross section for e+e− → ωπ0 → π0π0γ at energies 0.92 and 1.38 GeV.

Source code:CMD2_2003_I616446.cc

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

namespace Rivet {


  /// @brief Add a short analysis description here
  class CMD2_2003_I616446 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CMD2_2003_I616446);


    /// @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);
    }


    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;
      }
      // 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(round(sqrtS()/MeV));
    }
      }
    }


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

    /// @name Histograms
    /// @{
    BinnedHistoPtr<int> _numOmegaPi;
    /// @}

  };


  RIVET_DECLARE_PLUGIN(CMD2_2003_I616446);


}