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 JADE_1982_I177090 : public Analysis {
 12  public:
 13
 14    /// Constructor
 15    RIVET_DEFAULT_ANALYSIS_CTOR(JADE_1982_I177090);
 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(), "UFS");
 27      // book the histograms
 28      book(_h_etap,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    /// Perform the per-event analysis
 62    void analyze(const Event& event) {
 63      // find scattered leptons and calc Q2
 64      const Beam& beams = apply<Beam>(event, "Beams");
 65      double q12 = -1, q22 = -1;
 66      if (!findScattered(beams.beams().first,  q12)) vetoEvent;
 67      if (!findScattered(beams.beams().second, q22)) vetoEvent;
 68      // check the final state
 69      const FinalState & fs = apply<FinalState>(event, "FS");
 70      map<long,int> nCount;
 71      int ntotal(0);
 72      for (const Particle& p : fs.particles()) {
 73        nCount[p.pid()] += 1;
 74        ++ntotal;
 75      }
 76      // find the meson
 77      const FinalState& ufs = apply<FinalState>(event, "UFS");
 78      for (const Particle& p : ufs.particles(Cuts::pid==331)) {
 79        if(p.children().empty()) continue;
 80        map<long,int> nRes = nCount;
 81        int ncount = ntotal;
 82        findChildren(p,nRes,ncount);
 83        bool matched = true;
 84        for(auto const & val : nRes) {
 85          if(abs(val.first)==11) {
 86            if(val.second!=1) {
 87              matched = false;
 88              break;
 89            }
 90          }
 91          else if(val.second!=0) {
 92            matched = false;
 93            break;
 94          }
 95        }
 96        if (matched) {
 97          _h_etap->fill(sqrtS());
 98          break;
 99        }
100      }
101    }
102
103
104    /// Normalise histograms etc., after the run
105    void finalize() {
106      // need to undo bin width in result
107      const double binWidth=10.2;
108      scale(_h_etap, binWidth*crossSection()/nanobarn/sumW());
109    }
110
111    /// @}
112
113
114    /// @name Histograms
115    /// @{
116    Histo1DPtr _h_etap;
117    /// @}
118
119
120  };
121
122
123  RIVET_DECLARE_PLUGIN(JADE_1982_I177090);
124
125}