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 J/psi
 10  class BESIII_2023_I2617922 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2023_I2617922);
 15
 16
 17    /// @name Analysis methods
 18    /// @{
 19
 20    /// Book histograms and initialise projections before the run
 21    void init() {
 22      declare(FinalState(), "FS");
 23      declare(UnstableParticles(), "UFS");
 24      book(_nJPsi,1,1,1);
 25    }
 26
 27    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 28      for (const Particle &child : p.children()) {
 29        if (child.children().empty()) {
 30          --nRes[child.pid()];
 31          --ncount;
 32        }
 33        else {
 34          findChildren(child,nRes,ncount);
 35        }
 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      map<long,int> nCount;
 44      int ntotal(0);
 45      for (const Particle& p : fs.particles()) {
 46        nCount[p.pid()] += 1;
 47        ++ntotal;
 48      }
 49      const FinalState& ufs = apply<FinalState>(event, "UFS");
 50      for (const Particle& p : ufs.particles(Cuts::pid==PID::JPSI)) {
 51        if (p.children().empty()) continue;
 52        // find the J/psi
 53        map<long,int> nRes = nCount;
 54        int ncount = ntotal;
 55        findChildren(p,nRes,ncount);
 56        bool matched=false;
 57        for (const Particle& p2 : ufs.particles(Cuts::pid==PID::ETA)) {
 58          if (p2.children().empty()) continue;
 59          bool JpsiParent=false;
 60          Particle parent=p2;
 61          while (!parent.parents().empty()) {
 62            parent=parent.parents()[0];
 63            if (parent.pid()==PID::JPSI) {
 64              JpsiParent=true;
 65              break;
 66            }
 67          }
 68          if (JpsiParent) continue;
 69          map<long,int> nRes2 = nRes;
 70          int ncount2 = ncount;
 71          findChildren(p2,nRes2,ncount2);
 72          if(ncount2!=0) continue;
 73          matched = true;
 74          for (const auto& val : nRes2) {
 75            if (val.second!=0) {
 76              matched = false;
 77              break;
 78            }
 79          }
 80          if (matched) {
 81            _nJPsi->fill("3.773"s);
 82            break;
 83          }
 84        }
 85        if (matched) break;
 86      }
 87    }
 88
 89
 90    /// Normalise histograms etc., after the run
 91    void finalize() {
 92      scale(_nJPsi,crossSection()/ sumOfWeights() /picobarn);
 93    }
 94
 95    /// @}
 96
 97
 98    /// @name Histograms
 99    /// @{
100    BinnedHistoPtr<string> _nJPsi;
101    /// @}
102
103
104  };
105
106
107  RIVET_DECLARE_PLUGIN(BESIII_2023_I2617922);
108
109}