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-> gamama eta_c
 10  class BESIII_2017_I1600581 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2017_I1600581);
 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(Cuts::pid==441), "UFS");
 24      book(_sigmaEta, 1,1,1);
 25
 26      for (const string& en : _sigmaEta.binning().edges<0>()) {
 27        const double end = std::stod(en)*GeV;
 28        if (isCompatibleWithSqrtS(end)) {
 29          _ecms = en;
 30          break;
 31        }
 32      }
 33      if (_ecms.empty()) MSG_ERROR("Beam energy incompatible with analysis.");
 34    }
 35
 36    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 37      for (const Particle &child : p.children()) {
 38        if (child.children().empty()) {
 39          --nRes[child.pid()];
 40          --ncount;
 41        }
 42        else {
 43          findChildren(child,nRes,ncount);
 44        }
 45      }
 46    }
 47
 48    /// Perform the per-event analysis
 49    void analyze(const Event& event) {
 50      const FinalState& fs = apply<FinalState>(event, "FS");
 51      map<long,int> nCount;
 52      int ntotal(0);
 53      for (const Particle& p : fs.particles()) {
 54        nCount[p.pid()] += 1;
 55        ++ntotal;
 56      }
 57      const FinalState& ufs = apply<FinalState>(event, "UFS");
 58      for (const Particle& p : ufs.particles()) {
 59        if (p.children().empty()) continue;
 60        // find the chi_c
 61        map<long,int> nRes = nCount;
 62        int ncount = ntotal;
 63        findChildren(p,nRes,ncount);
 64        bool matched=true;
 65        if (ncount!=1) continue;
 66        for (const auto& val : nRes) {
 67          if (val.first==PID::PHOTON) {
 68            if (val.second!=1) {
 69              matched = false;
 70              break;
 71            }
 72          }
 73          else if (val.second!=0) {
 74            matched = false;
 75            break;
 76          }
 77        }
 78        if (matched) {
 79          _sigmaEta->fill(_ecms);
 80          break;
 81        }
 82      }
 83    }
 84
 85
 86    /// Normalise histograms etc., after the run
 87    void finalize() {
 88      scale(_sigmaEta, crossSection()/ sumOfWeights() /picobarn);
 89    }
 90
 91    /// @}
 92
 93
 94    /// @name Histograms
 95    /// @{
 96    BinnedHistoPtr<string> _sigmaEta;
 97    string _ecms;
 98    /// @}
 99
100
101  };
102
103
104  RIVET_DECLARE_PLUGIN(BESIII_2017_I1600581);
105
106}