1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/FinalState.hh"
  4#include "Rivet/Projections/UnstableParticles.hh"
  5
  6namespace Rivet {
  7
  8
  9  /// @brief e+e- > eta eta gamma cross section
 10  class SND_2021_I1942539 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(SND_2021_I1942539);
 15
 16
 17    /// @name Analysis methods
 18    ///@{
 19
 20    /// Book histograms and initialise projections before the run
 21    void init() {
 22      // Initialise and register projections
 23      declare(FinalState(), "FS");
 24      declare(UnstableParticles(), "UFS");
 25      book(_numEtaEtaGamma, "TMP/EtaEtaGamma");
 26    }
 27
 28    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 29      for (const Particle &child : p.children()) {
 30	if(child.children().empty()) {
 31	  --nRes[child.pid()];
 32	  --ncount;
 33	}
 34	else
 35	  findChildren(child,nRes,ncount);
 36      }
 37    }
 38
 39    /// Perform the per-event analysis
 40    void analyze(const Event& event) {
 41      const FinalState& fs = apply<FinalState>(event, "FS");
 42
 43      map<long,int> nCount;
 44      int ntotal(0);
 45      for (const Particle& p : fs.particles()) {
 46	nCount[p.pid()] += 1;
 47	++ntotal;
 48      }
 49	 
 50      Particles etas = apply<FinalState>(event, "UFS").particles(Cuts::pid==221);
 51      // find the first eta
 52      for(unsigned int ix=0;ix<etas.size();++ix) {
 53	bool matched = false;
 54	if(etas[ix].children().empty()) continue;
 55	map<long,int> nRes = nCount;
 56	int ncount = ntotal;
 57	findChildren(etas[ix],nRes,ncount);
 58	// find the second eta
 59	for(unsigned int iy=ix+1;iy<etas.size();++iy) {
 60	  if(etas[iy].children().empty()) continue;
 61	  map<long,int> nResB = nRes;
 62	  int ncountB = ncount;
 63	  findChildren(etas[iy],nResB,ncountB);
 64	  matched = true;
 65	  for(auto const & val : nResB) {
 66	    if(val.first==22) {
 67	      if(val.second !=1) {
 68		matched = false;
 69		break;
 70	      }
 71	    }
 72	    else if(val.second!=0) {
 73	      matched = false;
 74	      break;
 75	    }
 76	  }
 77	  if(matched) {
 78	    _numEtaEtaGamma->fill();
 79	    break;
 80	  }
 81	}
 82	if(matched) break;
 83      }
 84    }
 85
 86
 87    /// Normalise histograms etc., after the run
 88    void finalize() {
 89      double sigma = _numEtaEtaGamma->val();
 90      double error = _numEtaEtaGamma->err();
 91      sigma *= crossSection()/ sumOfWeights() /picobarn;
 92      error *= crossSection()/ sumOfWeights() /picobarn;
 93      Estimate1DPtr mult;
 94      book(mult, 1, 1, 1);
 95      for (auto& b : mult->bins()) {
 96        if (inRange(sqrtS()/GeV, b.xMin(), b.xMax())) {
 97          b.set(sigma, error);
 98        }
 99      }
100    }
101
102    ///@}
103
104
105    /// @name Histograms
106    ///@{
107    CounterPtr _numEtaEtaGamma;
108    ///@}
109
110
111  };
112
113
114  RIVET_DECLARE_PLUGIN(SND_2021_I1942539);
115
116}