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- > pi+pi- eta'
 10  class BESIII_2020_I1836509 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1836509);
 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      // histograms
 26      book(_nPiPiEta, "/TMP/nPiPiEta");
 27    }
 28
 29    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 30      for(const Particle &child : p.children()) {
 31	if(child.children().empty()) {
 32	  nRes[child.pid()]-=1;
 33	  --ncount;
 34	}
 35	else
 36	  findChildren(child,nRes,ncount);
 37      }
 38    }
 39
 40    /// Perform the per-event analysis
 41    void analyze(const Event& event) {
 42      const FinalState& fs = apply<FinalState>(event, "FS");
 43
 44      map<long,int> nCount;
 45      int ntotal(0);
 46      for (const Particle& p : fs.particles()) {
 47	nCount[p.pid()] += 1;
 48	++ntotal;
 49      }
 50      const FinalState& ufs = apply<FinalState>(event, "UFS");
 51      for (const Particle& p : ufs.particles(Cuts::pid==331)) {
 52	if(p.children().empty()) continue;
 53	map<long,int> nRes = nCount;
 54	int ncount = ntotal;
 55	findChildren(p,nRes,ncount);
 56	if(ncount!=2) continue;
 57	bool matched = true;
 58	for(auto const & val : nRes) {
 59	  if(abs(val.first)==211) {
 60	    if(val.second!=1) {
 61	      matched = false;
 62	      break;
 63	    }
 64	  }
 65	  else if(val.second!=0) {
 66	    matched = false;
 67	    break;
 68	  }
 69	}
 70	if(matched) _nPiPiEta->fill();
 71      }
 72    }
 73
 74
 75    /// Normalise histograms etc., after the run
 76    void finalize() {
 77      double sigma = _nPiPiEta->val();
 78      double error = _nPiPiEta->err();
 79      sigma *= crossSection()/ sumOfWeights() /picobarn;
 80      error *= crossSection()/ sumOfWeights() /picobarn;
 81      Estimate1DPtr  mult;
 82      book(mult, 1, 1, 1);
 83      for (auto& b : mult->bins()) {
 84        if (inRange(sqrtS()/GeV, b.xMin(), b.xMax())) {
 85          b.set(sigma, error);
 86        }
 87      }
 88    }
 89    ///@}
 90
 91
 92    /// @name Histograms
 93    ///@{
 94    CounterPtr _nPiPiEta;
 95    ///@}
 96
 97
 98  };
 99
100
101  RIVET_DECLARE_PLUGIN(BESIII_2020_I1836509);
102
103}