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 Lambda Lambdabar cross section
 10  class BESIII_2021_I1900124 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1900124);
 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(_nLambda, "/TMP/nLambda" );
 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()]-=1;
 32	  --ncount;
 33	}
 34	else
 35	  findChildren(child,nRes,ncount);
 36      }
 37    }
 38
 39
 40    /// Perform the per-event analysis
 41    void analyze(const Event& event) {
 42      const FinalState& fs = apply<FinalState>(event, "FS");
 43      // total hadronic and muonic cross sections
 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      // find the Lambdas
 51      const FinalState& ufs = apply<UnstableParticles>(event, "UFS");
 52      for(unsigned int ix=0;ix<ufs.particles().size();++ix) {
 53	const Particle& p1 = ufs.particles()[ix];
 54	if(abs(p1.pid())!=3122) continue;
 55	bool matched = false;
 56	// check fs
 57	bool fs = true;
 58	for (const Particle & child : p1.children()) {
 59	  if(child.pid()==p1.pid()) {
 60	    fs = false;
 61	    break;
 62	  }
 63	}
 64	if(!fs) continue;
 65	// find the children
 66	map<long,int> nRes = nCount;
 67	int ncount = ntotal;
 68	findChildren(p1,nRes,ncount);
 69	for(unsigned int iy=ix+1;iy<ufs.particles().size();++iy) {
 70	  const Particle& p2 = ufs.particles()[iy];
 71	  if(abs(p2.pid())!=3122) continue;
 72	  // check fs
 73	  bool fs = true;
 74	  for (const Particle & child : p2.children()) {
 75	    if(child.pid()==p2.pid()) {
 76	      fs = false;
 77	      break;
 78	    }
 79	  }
 80	  if(!fs) continue;
 81	  map<long,int> nRes2 = nRes;
 82	  int ncount2 = ncount;
 83	  findChildren(p2,nRes2,ncount2);
 84	  if(ncount2!=0) continue;
 85	  matched=true;
 86	  for(auto const & val : nRes2) {
 87	    if(val.second!=0) {
 88	      matched = false;
 89	      break;
 90	    }
 91	  }
 92	  if(matched) {
 93	    _nLambda->fill();
 94	    break;
 95	  }
 96	}
 97	if(matched) break;
 98      }
 99    }
100
101
102    /// Normalise histograms etc., after the run
103    void finalize() {
104      double sigma = _nLambda->val();
105      double error = _nLambda->err();
106      sigma *= crossSection()/ sumOfWeights() /femtobarn;
107      error *= crossSection()/ sumOfWeights() /femtobarn;
108      Estimate1DPtr  mult;
109      book(mult, 1, 1, 1);
110      for (auto& b : mult->bins()) {
111        if (inRange(sqrtS()/GeV, b.xMin(), b.xMax())) {
112          b.set(sigma, error);
113        }
114      }
115    }
116
117    ///@}
118
119
120    /// @name Histograms
121    ///@{
122    CounterPtr _nLambda;
123    ///@}
124
125
126  };
127
128
129  RIVET_DECLARE_PLUGIN(BESIII_2021_I1900124);
130
131}