Rivet analyses

Cross section for e+e− → ωπ+π− between 2 and 3.08 GeV

Experiment: BESIII (BEPC)

Inspire ID: 2133889

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2208.04507

Beams: e+ e-

Beam energies: (1.0, 1.0); (1.0, 1.0); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.2, 1.2); (1.2, 1.2); (1.2, 1.2); (1.3, 1.3); (1.3, 1.3); (1.4, 1.4); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5)GeV

Run details: - e+e- to hadrons

Measurement of the cross section for e+e− → ωπ+π− between 2 and 3.08 GeV by the BESIII collaboration. The cross section for a number of resonant intermediate states are also measured.

Source code:BESIII_2022_I2133889.cc

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

namespace Rivet {


  /// @brief e+e- -> omega pi+ pi-
  class BESIII_2022_I2133889 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2133889);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      book(_sigma[0], 1, 1, 1);
      for (size_t ix=1; ix<7; ++ix) {
        book(_sigma[ix], 2, 1, ix);
        if (ix < 3) {
          for (const string& en : _sigma[ix-1].binning().edges<0>()) {
            const double eval = stod(en)*GeV;
            if (isCompatibleWithSqrtS(eval)) {
              _sqs[ix-1] = en; break;
            }
          }
        }
      }
      raiseBeamErrorIf(_sqs[0].empty() && _sqs[1].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()];
          --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");
      bool hasOmegaPiPi=false, hasResonance=false;
      for (const Particle& p : ufs.particles(Cuts::pid==223)) {
        if (p.children().empty()) continue;
        map<long,int> nRes = nCount;
        int ncount = ntotal;
        findChildren(p,nRes,ncount);
        // first the omega pi pi final state
        if (ncount==2) {
          hasOmegaPiPi=true;
          for (const auto& val : nRes) {
            if (abs(val.first)==211) {
              if (val.second !=1) {
                hasOmegaPiPi = false;
                break;
              }
            }
            else if(val.second!=0) {
              hasOmegaPiPi = false;
              break;
            }
          }
          if (hasOmegaPiPi) _sigma[0]->fill(_sqs[0]);
        }
        // now omega + second resonance
        for (const Particle& p2 : ufs.particles(Cuts::pid==9000221||
                                                Cuts::pid==9010221||
                                                Cuts::pid==10221||
                                                Cuts::pid==225)) {
          if (p2.children().empty()) continue;
          map<long,int> nRes2 = nRes;
          int ncount2 = ncount;
          findChildren(p2,nRes2,ncount2);
          hasResonance=true;
          if (ncount2!=0) continue;
          for (const auto& val : nRes2) {
            if (val.second!=0) {
              hasResonance = false;
              break;
            }
          }
          if (hasResonance) {
            if      (p2.pid()==9000221 ) _sigma[1]->fill(_sqs[1]);
            else if (p2.pid()==9010221 ) _sigma[2]->fill(_sqs[1]);
            else if (p2.pid()==10221   ) _sigma[3]->fill(_sqs[1]);
            else if (p2.pid()==225     ) _sigma[4]->fill(_sqs[1]);
            break;
          }
        }
        if (hasOmegaPiPi) break;
      }
      if (hasResonance) return;
      // b_1 pi
      for (const Particle& p : ufs.particles(Cuts::abspid==10213)) {
        if (p.children().empty()) continue;
        map<long,int> nRes = nCount;
        int ncount = ntotal;
        findChildren(p,nRes,ncount);
        if (ncount!=1) continue;
        int ipi = -p.pid()/p.abspid()*211;
        hasResonance=true;
        for (const auto& val : nRes) {
          if (val.first==ipi) {
            if (val.second !=1) {
              hasOmegaPiPi = false;
              break;
            }
          }
          else if (val.second!=0) {
            hasResonance = false;
            break;
          }
        }
        if (hasResonance) {
          _sigma[5]->fill(_sqs[1]);
          break;
        }
      }
      if (hasOmegaPiPi && !hasResonance) _sigma[6]->fill(_sqs[1]);
    }


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

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _sigma[7];
    string _sqs[2];
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BESIII_2022_I2133889);

}