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(auto const & 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);


}