1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/Beam.hh"
  4#include "Rivet/Projections/UnstableParticles.hh"
  5#include "Rivet/Projections/DecayedParticles.hh"
  6
  7namespace Rivet {
  8
  9
 10  /// @brief J/psi -> gamma eta KS0,KS0
 11  class BESIII_2015_I1376282 : public Analysis {
 12  public:
 13
 14    /// Constructor
 15    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2015_I1376282);
 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      UnstableParticles ufs = UnstableParticles(Cuts::abspid==443);
 25      declare(ufs, "UFS");
 26      DecayedParticles PSI(ufs);
 27      PSI.addStable(PID::K0S);
 28      PSI.addStable(PID::ETA);
 29      declare(PSI, "PSI");
 30      declare(Beam(), "Beams");
 31      // Book histograms
 32      for(unsigned int ix=0;ix<6;++ix)
 33	book(_h[ix],1,1,1+ix);
 34    }
 35
 36    // angle cuts due regions of BES calorimeter
 37    bool vetoPhoton(const double & cTheta) {
 38      return cTheta>0.92 || (cTheta>0.8 && cTheta<0.86);
 39    }
 40
 41    /// Perform the per-event analysis
 42    void analyze(const Event& event) {
 43      // get the axis, direction of incoming electron
 44      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
 45      Vector3 axis;
 46      if(beams.first.pid()>0)
 47	axis = beams.first .momentum().p3().unit();
 48      else
 49	axis = beams.second.momentum().p3().unit();
 50      // find the J/psi decays
 51      static const map<PdgId,unsigned int> & mode = { { 221,1}, { 310,2},{ 22,1}};
 52      DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
 53      if( PSI.decaying().size()!=1) vetoEvent;
 54      if(!PSI.modeMatches(0,4,mode)) vetoEvent;
 55      const Particle  & eta = PSI.decayProducts()[0].at(221)[0];
 56      const Particles & K0  = PSI.decayProducts()[0].at(310);
 57      const Particle  & gam = PSI.decayProducts()[0].at( 22)[0];
 58      _h[0]->fill((K0[0].momentum()+K0[1].momentum()+eta.momentum()).mass());
 59      _h[1]->fill((K0[0].momentum()+K0[1].momentum()).mass());
 60      for(unsigned int ix=0;ix<2;++ix)
 61	_h[2]->fill((K0[ix].momentum()+eta.momentum()).mass());
 62      double cTheta = axis.dot(gam.p3().unit());
 63      // photon angle
 64      if(vetoPhoton(abs(cTheta))) vetoEvent;
 65      _h[3]->fill(cTheta);
 66      // remaining angles
 67      LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(PSI.decaying()[0].momentum().betaVec());
 68      FourMomentum pGamma    = boost1.transform(gam.momentum());
 69      FourMomentum pHadron = boost1.transform(K0[0].momentum()+K0[1].momentum()+eta.momentum());
 70      LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pHadron.betaVec());
 71      Vector3 axis1 = pGamma.p3().unit();
 72      Vector3 axis2 = boost2.transform(boost1.transform(eta.momentum()));
 73      _h[4]->fill(axis1.dot(axis2));
 74      FourMomentum pKK = boost2.transform(K0[0].momentum()+K0[1].momentum());
 75      LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(pKK.betaVec());
 76      for(unsigned ix=0;ix<2;++ix) {
 77	Vector3 axis3 = boost3.transform(boost2.transform(boost1.transform(K0[ix].momentum()))).p3().unit();
 78	_h[5]->fill(axis3.dot(axis2));
 79      }
 80    }
 81
 82
 83    /// Normalise histograms etc., after the run
 84    void finalize() {
 85      for(unsigned int ix=0;ix<6;++ix)
 86	normalize(_h[ix],1.,false);
 87    }
 88
 89    /// @}
 90
 91    /// @name Histograms
 92    /// @{
 93    Histo1DPtr _h[6];
 94    /// @}
 95
 96
 97  };
 98
 99
100  RIVET_DECLARE_PLUGIN(BESIII_2015_I1376282);
101
102}