Rivet analyses

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

namespace Rivet {


  /// @brief e+ e- > eta(') gamma
  class BABAR_2006_I716277 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2006_I716277);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      book(_numEtaGamma, 1, 1, 1);
      book(_numEtaPrimeGamma, 1, 1, 2);
    }

    void findChildren(const Particle& p, map<long, int>& nRes, int& ncount) {
      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");
      for (const Particle& p : ufs.particles()) {
        if (p.children().empty()) continue;
        // find the eta/eta prime
        if (p.pid() != 221 && p.pid() != 331) continue;
        map<long, int> nRes = nCount;
        int ncount = ntotal;
        findChildren(p, nRes, ncount);
        // eta pi+pi-
        if (ncount != 1) continue;
        bool matched = true;
        for (const auto& val : nRes) {
          if (val.first == 22) {
            if (val.second != 1) {
              matched = false;
              break;
            }
          }
          else if (val.second != 0) {
            matched = false;
            break;
          }
        }
        if (matched) {
          if (p.pid() == 221)
            _numEtaGamma->fill("10.58"s);
          else
            _numEtaPrimeGamma->fill("10.58"s);
        }
      }
    }

    /// Normalise histograms etc., after the run
    void finalize() {
      double fact = crossSection() / sumOfWeights() / femtobarn;
      scale(_numEtaGamma, fact);
      scale(_numEtaPrimeGamma, fact);
    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _numEtaGamma, _numEtaPrimeGamma;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BABAR_2006_I716277);


}