Rivet analyses

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

namespace Rivet {


  /// @brief e+e- > eta omega and omega pi0
  class BESIII_2022_I2047667 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2047667);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      for (size_t ix=0; ix<2; ++ix) {
        book(_nMeson[ix], 1, 1, 1+ix);
      }
      for (const string& en : _nMeson[0].binning().edges<0>()) {
        const double end = stod(en)*GeV;
        if (isCompatibleWithSqrtS(end)) {
          _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()];
          --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 UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      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);
        if (ncount==1) {
          bool matched=true;
          for (const auto& val : nRes) {
            if (val.first==111 ) {
              if (val.second !=1) {
                matched = false;
                break;
              }
            }
            else if(val.second!=0) {
              matched = false;
              break;
            }
          }
          if (matched) {
            _nMeson[0]->fill(_sqs);
            continue;
          }
        }
        else {
          // check for eta
          for (const Particle& p2 : ufs.particles(Cuts::pid==221)) {
            map<long,int> nResB = nRes;
            int ncountB = ncount;
            findChildren(p2,nResB,ncountB);
            if (ncountB!=0) continue;
            bool matched = true;
            for (const auto& val : nResB) {
              if (val.second!=0) {
                matched = false;
                break;
              }
            }
            if(matched) {
              _nMeson[1]->fill(_sqs);
              break;
            }
          }
        }
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _nMeson[2];
    string _sqs = "";
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BESIII_2022_I2047667);

}