Rivet analyses

Cross section for e⁺e⁻ → 2π⁺2π⁻ and π⁺π⁻2π⁰ below 1.38 GeV

Experiment: CMD2 (VEPP-2M)

Inspire ID: 483994

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett. B466 (1999) 392-402, 199 9

Beams: e+ e-

Beam energies: ANY

Run details: - e+e- to hadrons

Measurement of the cross section for e⁺e⁻ → 2π⁺2π⁻ and π⁺π⁻2π⁰ below 1.38 GeV

Source code:`CMD2_1999_I483994.cc`

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


namespace Rivet {


  /// @brief e+e- -> 4 pions
  class CMD2_1999_I483994 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CMD2_1999_I483994);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      book(_ncharged, 1, 1, 1);
      book(_nneutral, 2, 1, 1);
      book(_nomega  , 3, 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()];
      --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==4) {
    if( nCount[211] == 2 && nCount[-211] == 2 )
      _ncharged->fill(round(sqrtS()/MeV));
    else if( nCount[211] == 1 && nCount[-211] == 1 && nCount[111] == 2)
      _nneutral->fill(round(sqrtS()/MeV));
      }


      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 = nCount;
      int ncount = ntotal;
      findChildren(p,nRes,ncount);
      // omega pi+pi-
      if(ncount!=1) continue;
      bool matched = true;
      for(auto const & val : nRes) {
        if(abs(val.first)==111) {
          if(val.second !=1) {
        matched = false;
        break;
          }
        }
        else if(val.second!=0) {
          matched = false;
          break;
        }
      }
      if(matched)
        _nomega->fill(round(sqrtS()/MeV));
    }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      double fact = crossSection()/ sumOfWeights() /nanobarn;
      scale(_ncharged,fact);
      scale(_nneutral,fact);
      scale(_nomega  ,fact);
    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<int> _ncharged,_nneutral,_nomega;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(CMD2_1999_I483994);


}

Rivet analyses

Cross section for e+e− → 2π+2π− and π+π−2π0 below 1.38 GeV

Source code:CMD2_1999_I483994.cc

Cross section for e⁺e⁻ → 2π⁺2π⁻ and π⁺π⁻2π⁰ below 1.38 GeV

Source code:`CMD2_1999_I483994.cc`