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- > phi eta
 10  class BESIII_2021_I1857930 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1857930);
 15
 16
 17    /// @name Analysis methods
 18    ///@{
 19
 20    /// Book histograms and initialise projections before the run
 21    void init() {
 22
 23      // Initialise and register projections
 24      declare(FinalState(), "FS");
 25      declare(UnstableParticles(), "UFS");
 26      book(_nPhiEta,"/TMP/_nPhiEta");
 27
 28    }
 29
 30    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 31      for (const Particle &child : p.children()) {
 32	if(child.children().empty()) {
 33	  nRes[child.pid()]-=1;
 34	  --ncount;
 35	}
 36	else
 37	  findChildren(child,nRes,ncount);
 38      }
 39    }
 40
 41
 42    /// Perform the per-event analysis
 43    void analyze(const Event& event) {
 44      const FinalState& fs = apply<FinalState>(event, "FS");
 45
 46      map<long,int> nCount;
 47      int ntotal(0);
 48      for (const Particle& p : fs.particles()) {
 49	nCount[p.pid()] += 1;
 50	++ntotal;
 51      }
 52      const FinalState& ufs = apply<FinalState>(event, "UFS");
 53
 54      // loop over eta mesons
 55      for (const Particle& p : ufs.particles(Cuts::pid==221)) {
 56	if(p.children().empty()) continue;
 57	map<long,int> nRes = nCount;
 58	int ncount = ntotal;
 59	findChildren(p,nRes,ncount);
 60	// loop over phi mesons
 61	for (const Particle& p2 : ufs.particles(Cuts::pid==333)) {
 62	  if(p2.parents()[0].isSame(p)) continue;
 63	  map<long,int> nResB = nRes;
 64	  int ncountB = ncount;
 65	  findChildren(p2,nResB,ncountB);
 66	  if(ncountB!=0) continue;
 67	  bool matched = true;
 68	  for(auto const & val : nResB) {
 69	    if(val.second!=0) {
 70	      matched = false;
 71	      break;
 72	    }
 73	  }
 74	  if(matched) _nPhiEta->fill();
 75	}
 76      }
 77    }
 78
 79
 80    /// Normalise histograms etc., after the run
 81    void finalize() {
 82      double sigma = _nPhiEta->val();
 83      double error = _nPhiEta->err();
 84      sigma *= crossSection()/ sumOfWeights()/picobarn;
 85      error *= crossSection()/ sumOfWeights()/picobarn;
 86      Estimate1DPtr  mult;
 87      book(mult, 1, 1, 1);
 88      for (auto& b : mult->bins()) {
 89        if (inRange(sqrtS()/GeV, b.xMin(), b.xMax())) {
 90          b.set(sigma, error);
 91        }
 92      }
 93    }
 94
 95    ///@}
 96
 97
 98    /// @name Histograms
 99    ///@{
100    CounterPtr _nPhiEta;
101    ///@}
102
103
104  };
105
106
107  RIVET_DECLARE_PLUGIN(BESIII_2021_I1857930);
108
109}