Rivet analyses

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

namespace Rivet {


  /// @brief Cross section for e+e- > gamma eta
  class SND_2014_I1275333 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(SND_2014_I1275333);


    /// @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, "TMP/EtaGamma", refData(1,1,1));
    }

    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(Cuts::pid==221)) {
    if(p.children().empty()) continue;
    // find the eta
    map<long,int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p,nRes,ncount);
    // eta gamma
    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)
      _numEtaGamma->fill(sqrtS()/MeV);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_numEtaGamma, crossSection()/ sumOfWeights() /picobarn);
      Estimate1DPtr tmp;
      book(tmp,1,1,1);
      barchart(_numEtaGamma,tmp);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _numEtaGamma;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(SND_2014_I1275333);


}