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 phi phi
 11  class BESIII_2016_I1419650 : public Analysis {
 12  public:
 13
 14    /// Constructor
 15    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2016_I1419650);
 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::PHI);
 28      declare(PSI, "PSI");
 29      declare(Beam(), "Beams");
 30      // book histograms
 31      for(unsigned int ix=0;ix<5;++ix)
 32	book(_h[ix],1,1,1+ix);
 33    }
 34
 35    // angle cuts due regions of BES calorimeter
 36    bool vetoPhoton(const double & cTheta) {
 37      return cTheta>0.92 || (cTheta>0.8 && cTheta<0.86);
 38    }
 39
 40    /// Perform the per-event analysis
 41    void analyze(const Event& event) {
 42      // get the axis, direction of incoming electron
 43      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
 44      Vector3 axis;
 45      if(beams.first.pid()>0)
 46	axis = beams.first .momentum().p3().unit();
 47      else
 48	axis = beams.second.momentum().p3().unit();
 49      // find the J/psi decays
 50      static const map<PdgId,unsigned int> & mode = { { 333,2},{ 22,1}};
 51      DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
 52      if( PSI.decaying().size()!=1) vetoEvent;
 53      if(!PSI.modeMatches(0,3,mode)) vetoEvent;
 54      // particles
 55      const Particles & phi = PSI.decayProducts()[0].at(333);
 56      const Particle  & gam = PSI.decayProducts()[0].at( 22)[0];
 57      _h[0]->fill((phi[0].momentum()+phi[1].momentum()).mass());
 58      double cTheta = axis.dot(gam.p3().unit());
 59      if(vetoPhoton(abs(cTheta))) vetoEvent;
 60      _h[1]->fill(cTheta);
 61      // remaining angles
 62      LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(PSI.decaying()[0].momentum().betaVec());
 63      FourMomentum pGamma = boost1.transform(gam.momentum());
 64      FourMomentum pPhiPhi= boost1.transform(phi[0].momentum()+phi[1].momentum());
 65      Vector3 e1z = pGamma.p3().unit();
 66      Vector3 e1y = e1z.cross(axis).unit();
 67      Vector3 e1x = e1y.cross(e1z).unit();
 68      LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pPhiPhi.betaVec());
 69      Vector3 axis2 = boost2.transform(boost1.transform(phi[0].momentum())).p3().unit();
 70      _h[2]->fill(e1z.dot(axis2));
 71      // now for the phi decays
 72      Particle Km[2],Kp[2];
 73      FourMomentum pKp[2],pPhi[2];
 74      for(unsigned int ix=0;ix<2;++ix) {
 75	if(phi[ix].children().size()!=2|| phi[ix].children()[0].pid()!=-phi[ix].children()[1].pid() ||
 76	   phi[ix].children()[0].abspid()!=321) vetoEvent;
 77	Km[ix] = phi[ix].children()[0];
 78	Kp[ix] = phi[ix].children()[1];
 79	if(Kp[ix].pid()<0) swap(Km[ix],Kp[ix]);
 80	pKp[ix]  = boost2.transform(boost1.transform(Kp[ix].momentum()));
 81	pPhi[ix] = boost2.transform(boost1.transform(phi[ix].momentum()));
 82	LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(pPhi[ix].betaVec());
 83	pKp[ix] = boost3.transform(pKp[ix]);
 84      }
 85      double cK = axis2.dot(pKp[0].p3().unit());
 86      _h[3]->fill(cK);
 87      Vector3 Trans1 = pKp[0].p3() - cK*pKp[0].p3().mod()*axis2;
 88      Vector3 Trans2 = pKp[1].p3() - axis2.dot(pKp[1].p3())*axis2;
 89      double chi = atan(Trans1.cross(Trans2).dot(axis2)/Trans1.dot(Trans2));
 90      _h[4]->fill(abs(chi)/M_PI*180.);
 91    }
 92
 93
 94    /// Normalise histograms etc., after the run
 95    void finalize() {
 96      for(unsigned int ix=0;ix<5;++ix)
 97	normalize(_h[ix],1.,false);
 98    }
 99
100    /// @}
101
102
103    /// @name Histograms
104    /// @{
105    Histo1DPtr _h[5];
106    /// @}
107
108
109  };
110
111
112  RIVET_DECLARE_PLUGIN(BESIII_2016_I1419650);
113
114}