Rivet analyses

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

namespace Rivet {


  /// @brief e+ e- -> phi chi_c(1,2)
  class BESIII_2022_I2169640 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2169640);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      for (size_t ix = 0; ix < 2; ++ix) {
        book(_sigma[ix], 1, 1, 1 + ix);
      }
      for (const string& en : _sigma[0].binning().edges<0>()) {
        const double eval = stod(en) * GeV;
        if (isCompatibleWithSqrtS(eval)) {
          _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 FinalState& ufs = apply<FinalState>(event, "UFS");
      // loop over any phi mesons
      for (const Particle& phi : ufs.particles(Cuts::pid == 333)) {
        bool matched = false;
        if (phi.children().empty()) continue;
        map<long, int> nRes = nCount;
        int ncount = ntotal;
        findChildren(phi, nRes, ncount);
        for (const Particle& chi : ufs.particles(Cuts::pid == 20443 || Cuts::pid == 445)) {
          if (chi.children().empty()) continue;
          map<long, int> nRes2 = nRes;
          int ncount2 = ncount;
          findChildren(chi, nRes2, ncount2);
          matched = true;
          for (const auto& val : nRes2) {
            if (val.second != 0) {
              matched = false;
              break;
            }
          }
          if (!matched) continue;
          if (chi.pid() == 20443)
            _sigma[0]->fill(_sqs);
          else if (chi.pid() == 445)
            _sigma[1]->fill(_sqs);
          break;
        }
        if (matched) break;
      }
    }


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

    /// @}


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


  RIVET_DECLARE_PLUGIN(BESIII_2022_I2169640);

}