Rivet analyses

Cross section for e+e− → ϕπ+π− and ϕπ0π0 at 2.125 GeV

Experiment: BESIII (BEPC)

Inspire ID: 1651451

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 99 (2019) 1, 011101

Beams: e+ e-

Beam energies: (1.1, 1.1)GeV

Run details: - e+e- to hadrons

Measurement of the cross section for e+e− → ϕπ+π− and ϕπ0π0 at 2.125 GeV.

Source code:BESIII_2018_I1651451.cc

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

namespace Rivet {


  /// @brief  e+e- -> phi pi+ pi- and phi pi0 pi0
  class BESIII_2018_I1651451 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1651451);


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

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

      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      // histograms
      for (unsigned int ix=0; ix<2; ++ix) {
        book(_h[ix],1,1,ix+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(Cuts::pid==PID::PHI)) {
        if (p.children().empty()) continue;
        map<long,int> nRes=nCount;
        int ncount = ntotal;
        findChildren(p,nRes,ncount);
        // phi pi+pi-
        if (ncount==2) {
          bool matched = true;
          for (const auto& val : nRes) {
            if (abs(val.first)==211) {
              if (val.second!=1) {
                matched = false;
                break;
              }
            }
            else if (val.second!=0) {
              matched = false;
              break;
            }
          }
          if (matched) {
            _h[0]->fill("2.125"s);
            break;
          }
          matched = true;
          for (const auto& val : nRes) {
            if (abs(val.first)==111) {
              if (val.second!=2) {
                matched = false;
                break;
              }
            }
            else if(val.second!=0) {
              matched = false;
              break;
            }
          }
          if (matched) {
            _h[1]->fill("2.125"s);
            break;
          }
        }
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _h[2];
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BESIII_2018_I1651451);

}