1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/FinalState.hh"
  4#include "Rivet/Projections/UnstableParticles.hh"
  5#include "Rivet/Projections/Beam.hh"
  6
  7namespace Rivet {
  8
  9
 10  /// @brief e+e- -> e+e- eta
 11  class TPC_1986_I217503 : public Analysis {
 12  public:
 13
 14    /// Constructor
 15    RIVET_DEFAULT_ANALYSIS_CTOR(TPC_1986_I217503);
 16
 17
 18    /// @name Analysis methods
 19    /// @{
 20
 21    /// Book histograms and initialise projections before the run
 22    void init() {
 23      // Initialise and register projections
 24      declare(Beam(), "Beams");
 25      declare(FinalState(),"FS");
 26      declare(UnstableParticles(Cuts::pid==221), "UFS");
 27      // book the histograms
 28      book(_h_eta,1,1,1);
 29    }
 30
 31    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 32      for (const Particle &child : p.children()) {
 33        if (child.children().empty()) {
 34          --nRes[child.pid()];
 35          --ncount;
 36        } else {
 37          findChildren(child,nRes,ncount);
 38        }
 39      }
 40    }
 41
 42    bool findScattered(Particle beam, double& q2) {
 43      bool found = false;
 44      Particle scat = beam;
 45      while (!scat.children().empty()) {
 46        found = false;
 47        for (const Particle & p : scat.children()) {
 48          if (p.pid()==scat.pid()) {
 49            scat=p;
 50            found=true;
 51            break;
 52          }
 53        }
 54        if (!found) break;
 55      }
 56      if (!found) return false;
 57      q2 = -(beam.momentum() - scat.momentum()).mass2();
 58      return true;
 59    }
 60
 61
 62    /// Perform the per-event analysis
 63    void analyze(const Event& event) {
 64      // find scattered leptons and calc Q2
 65      const Beam& beams = apply<Beam>(event, "Beams");
 66      double q12 = -1, q22 = -1;
 67      if (!findScattered(beams.beams().first,  q12)) vetoEvent;
 68      if (!findScattered(beams.beams().second, q22)) vetoEvent;
 69      // check the final state
 70      const FinalState & fs = apply<FinalState>(event, "FS");
 71      map<long,int> nCount;
 72      int ntotal(0);
 73      for (const Particle& p : fs.particles()) {
 74        nCount[p.pid()] += 1;
 75        ++ntotal;
 76      }
 77      // find the meson
 78      const FinalState& ufs = apply<FinalState>(event, "UFS");
 79      for (const Particle& p : ufs.particles()) {
 80        if(p.children().empty()) continue;
 81        map<long,int> nRes = nCount;
 82        int ncount = ntotal;
 83        findChildren(p,nRes,ncount);
 84        bool matched = true;
 85        for (const auto& val : nRes) {
 86          if (abs(val.first)==11) {
 87            if(val.second!=1) {
 88              matched = false;
 89              break;
 90            }
 91          }
 92          else if (val.second!=0) {
 93            matched = false;
 94            break;
 95          }
 96        }
 97        if (matched) {
 98          _h_eta->fill(29);
 99          break;
100        }
101      }
102    }
103
104
105    /// Normalise histograms etc., after the run
106    void finalize() {
107      scale(_h_eta, crossSection()/nanobarn/sumW());
108    }
109
110    /// @}
111
112
113    /// @name Histograms
114    /// @{
115    BinnedHistoPtr<int> _h_eta;
116    /// @}
117
118
119  };
120
121
122  RIVET_DECLARE_PLUGIN(TPC_1986_I217503);
123
124}