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- pi0
 11  class BABAR_2009_I821653 : public Analysis {
 12  public:
 13
 14    /// Constructor
 15    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2009_I821653);
 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
 33    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
 34      for (const Particle &child : p.children()) {
 35        if (child.children().empty()) {
 36          --nRes[child.pid()];
 37          --ncount;
 38        } else {
 39          findChildren(child,nRes,ncount);
 40        }
 41      }
 42    }
 43
 44    bool findScattered(Particle beam, double& q2) {
 45      bool found = false;
 46      Particle scat = beam;
 47      while (!scat.children().empty()) {
 48        found = false;
 49        for (const Particle & p : scat.children()) {
 50          if (p.pid()==scat.pid()) {
 51            scat=p;
 52            found=true;
 53            break;
 54          }
 55        }
 56        if (!found) break;
 57      }
 58      if (!found) return false;
 59      q2 = -(beam.momentum() - scat.momentum()).mass2();
 60      return true;
 61    }
 62
 63    /// Perform the per-event analysis
 64    void analyze(const Event& event) {
 65      // find scattered leptons and calc Q2
 66      const Beam& beams = apply<Beam>(event, "Beams");
 67      double q12 = -1, q22 = -1;
 68      if (!findScattered(beams.beams().first,  q12)) vetoEvent;
 69      if (!findScattered(beams.beams().second, q22)) vetoEvent;
 70      double scale = max(q12,q22);
 71      // check the final state
 72      const FinalState & fs = apply<FinalState>(event, "FS");
 73      map<long,int> nCount;
 74      int ntotal(0);
 75      for (const Particle& p : fs.particles()) {
 76        nCount[p.pid()] += 1;
 77        ++ntotal;
 78      }
 79      // find the meson
 80      const FinalState& ufs = apply<FinalState>(event, "UFS");
 81      for (const Particle& p : ufs.particles(Cuts::pid==111)) {
 82        if(p.children().empty()) continue;
 83        map<long,int> nRes = nCount;
 84        int ncount = ntotal;
 85        findChildren(p,nRes,ncount);
 86        bool matched = true;
 87        for(auto const & val : nRes) {
 88          if(abs(val.first)==11) {
 89            if(val.second!=1) {
 90              matched = false;
 91              break;
 92            }
 93          }
 94          else if(val.second!=0) {
 95            matched = false;
 96            break;
 97          }
 98        }
 99        if (matched) {
100	  _h_pi0->fill(scale);
101          break;
102        }
103      }
104    }
105
106
107    /// Normalise histograms etc., after the run
108    void finalize() {
109      // normalize the cross sections
110      scale(_h_pi0, crossSection()/femtobarn/sumW());
111    }
112
113    ///@}
114
115
116    /// @name Histograms
117    ///@{
118    Histo1DPtr _h_pi0;
119    ///@}
120
121
122  };
123
124
125  RIVET_DECLARE_PLUGIN(BABAR_2009_I821653);
126
127}