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 BELLE  e+e- > e+e- pi0
 11  class BELLE_2012_I1114749 : public Analysis {
 12  public:
 13
 14    /// Constructor
 15    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2012_I1114749);
 16
 17
 18    /// @name Analysis methods
 19    ///@{
 20
 21    /// Book histograms and initialise projections before the run
 22    void init() {
 23
 24      // Initialise and register projections
 25      declare(Beam(), "Beams");
 26      declare(FinalState(),"FS");
 27      declare(UnstableParticles(), "UFS");
 28      // book the histograms
 29      book(_h_pi0,1,1,1);
 30    }
 31
 32    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 33      for (const Particle &child : p.children()) {
 34        if (child.children().empty()) {
 35          --nRes[child.pid()];
 36          --ncount;
 37        } else {
 38          findChildren(child,nRes,ncount);
 39        }
 40      }
 41    }
 42
 43    bool findScattered(Particle beam, double& q2) {
 44      bool found = false;
 45      Particle scat = beam;
 46      while (!scat.children().empty()) {
 47        found = false;
 48        for (const Particle & p : scat.children()) {
 49          if (p.pid()==scat.pid()) {
 50            scat=p;
 51            found=true;
 52            break;
 53          }
 54        }
 55        if (!found) break;
 56      }
 57      if (!found) return false;
 58      q2 = -(beam.momentum() - scat.momentum()).mass2();
 59      return true;
 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      double scale = max(q12,q22);
 70      // check the final state
 71      const FinalState & fs = apply<FinalState>(event, "FS");
 72      map<long,int> nCount;
 73      int ntotal(0);
 74      for (const Particle& p : fs.particles()) {
 75        nCount[p.pid()] += 1;
 76        ++ntotal;
 77      }
 78      // find the meson
 79      const FinalState& ufs = apply<FinalState>(event, "UFS");
 80      for (const Particle& p : ufs.particles(Cuts::pid==111)) {
 81        if(p.children().empty()) continue;
 82        map<long,int> nRes = nCount;
 83        int ncount = ntotal;
 84        findChildren(p,nRes,ncount);
 85        bool matched = true;
 86        for(auto const & val : nRes) {
 87          if(abs(val.first)==11) {
 88            if(val.second!=1) {
 89              matched = false;
 90              break;
 91            }
 92          }
 93          else if(val.second!=0) {
 94            matched = false;
 95            break;
 96          }
 97        }
 98        if (matched) {
 99	  _h_pi0->fill(scale);
100          break;
101        }
102      }
103    }
104
105
106    /// Normalise histograms etc., after the run
107    void finalize() {
108      // normalize the cross sections
109      scale(_h_pi0, crossSection()/femtobarn/sumW());
110    }
111
112    ///@}
113
114
115    /// @name Histograms
116    ///@{
117    Histo1DPtr _h_pi0;
118    ///@}
119
120
121  };
122
123
124  RIVET_DECLARE_PLUGIN(BELLE_2012_I1114749);
125
126}