Rivet analyses

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

namespace Rivet {


  /// @brief e+ e- > 2 phi + phi or omega
  class BESIII_2017_I1607253 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2017_I1607253);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(Cuts::pid == 223 || Cuts::pid == 333), "UFS");
      // counters
      for (size_t ix = 0; ix < 2; ++ix) {
        book(_sigma[ix], 1 + ix, 1, 1);
      }

      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");
      Particles phi = ufs.particles(Cuts::pid == 333);
      Particles omega = ufs.particles(Cuts::pid == 223);
      if (phi.size() < 2) vetoEvent;
      bool found = false;
      // first phi
      for (unsigned int ix = 0; ix < phi.size(); ++ix) {
        const Particle& phi1 = phi[ix];
        if (phi1.children().empty()) continue;
        map<long, int> nRes = nCount;
        int ncount = ntotal;
        findChildren(phi1, nRes, ncount);
        // second phi
        for (unsigned int iy = ix + 1; iy < phi.size(); ++iy) {
          const Particle& phi2 = phi[iy];
          if (phi2.children().empty()) continue;
          map<long, int> nRes2 = nRes;
          int ncount2 = ncount;
          findChildren(phi2, nRes2, ncount2);
          // search for third phi
          for (unsigned int iz = iy + 1; iz < phi.size(); ++iz) {
            const Particle& phi3 = phi[iz];
            if (phi3.children().empty()) continue;
            map<long, int> nRes3 = nRes2;
            int ncount3 = ncount2;
            findChildren(phi3, nRes3, ncount3);
            found = true;
            for (const auto& val : nRes3) {
              if (val.second != 0) {
                found = false;
                break;
              }
            }
            if (found) {
              _sigma[1]->fill(_sqs);
              break;
            }
          }
          if (found) break;
          // search for omega
          for (unsigned int iz = 0; iz < omega.size(); ++iz) {
            const Particle& omega1 = omega[iz];
            if (omega1.children().empty()) continue;
            map<long, int> nRes3 = nRes2;
            int ncount3 = ncount2;
            findChildren(omega1, nRes3, ncount3);
            found = true;
            for (const auto& val : nRes3) {
              if (val.second != 0) {
                found = false;
                break;
              }
            }
            if (found) {
              _sigma[0]->fill(_sqs);
              break;
            }
          }
          if (found) break;
        }
        if (found) break;
      }
    }


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

    /// @}


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


  RIVET_DECLARE_PLUGIN(BESIII_2017_I1607253);

}