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 omega omega
 11  class BESIII_2013_I1203841 : public Analysis {
 12  public:
 13
 14    /// Constructor
 15    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2013_I1203841);
 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      PSI.addStable(PID::OMEGA);
 29      declare(PSI, "PSI");
 30      declare(Beam(), "Beams");
 31      // histograms
 32      for(unsigned int ix=0;ix<9;++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    void findChildren(const Particle & p, Particles & pim, Particles & pip,
 42		      Particles & pi0, unsigned int &ncount) {
 43      for( const Particle &child : p.children()) {
 44	if(child.pid()==PID::PIPLUS) {
 45	  pip.push_back(child);
 46	  ncount+=1;
 47	}
 48	else if(child.pid()==PID::PIMINUS) {
 49	  pim.push_back(child);
 50	  ncount+=1;
 51	}
 52	else if(child.pid()==PID::PI0) {
 53	  pi0.push_back(child);
 54	  ncount+=1;
 55	}
 56	else if(child.children().empty()) {
 57	  ncount+=1;
 58	}
 59    	else
 60    	  findChildren(child,pim,pip,pi0,ncount);
 61      }
 62    }
 63
 64    /// Perform the per-event analysis
 65    void analyze(const Event& event) {
 66      // get the axis, direction of incoming electron
 67      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
 68      Vector3 axis;
 69      if(beams.first.pid()>0)
 70	axis = beams.first .momentum().p3().unit();
 71      else
 72	axis = beams.second.momentum().p3().unit();
 73      // find the J/psi decays
 74      static const map<PdgId,unsigned int> & mode = { { 223,1}, { 333,1},{ 22,1}};
 75      DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
 76      if( PSI.decaying().size()!=1) vetoEvent;
 77      if(!PSI.modeMatches(0,3,mode)) vetoEvent;
 78      // particles
 79      const Particle & phi   = PSI.decayProducts()[0].at(333)[0];
 80      const Particle & omega = PSI.decayProducts()[0].at(223)[0];
 81      const Particle & gam   = PSI.decayProducts()[0].at( 22)[0];
 82      _h[0]->fill((omega.momentum()+phi.momentum()).mass());
 83      _h[1]->fill((omega.momentum()+gam.momentum()).mass());
 84      _h[2]->fill((phi  .momentum()+gam.momentum()).mass());
 85      double cTheta = axis.dot(gam.p3().unit());
 86      if(vetoPhoton(abs(cTheta))) vetoEvent;
 87      _h[3]->fill(cTheta);
 88      // remaining angles
 89      LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(PSI.decaying()[0].momentum().betaVec());
 90      FourMomentum pGamma    = boost1.transform(gam.momentum());
 91      FourMomentum pOmegaPhi = boost1.transform(omega.momentum()+phi.momentum());
 92      Vector3 e1z = pGamma.p3().unit();
 93      Vector3 e1y = e1z.cross(axis).unit();
 94      Vector3 e1x = e1y.cross(e1z).unit();
 95      LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pOmegaPhi.betaVec());
 96      Vector3 axis2 = boost2.transform(boost1.transform(phi.momentum())).p3().unit();
 97      _h[5]->fill(e1z.dot(axis2));
 98      double phiPhi = atan2(axis2.dot(e1y),axis2.dot(e1x));
 99      if(phiPhi<0.) phiPhi+=2.*M_PI;
100      _h[7]->fill(phiPhi);
101      // now for the phi decays
102      if(phi.children().size()!=2|| phi.children()[0].pid()!=-phi.children()[1].pid() ||
103	 phi.children()[0].abspid()!=321) vetoEvent;
104      Particle Km = phi.children()[0];
105      Particle Kp = phi.children()[1];
106      if(Kp.pid()<0) swap(Km,Kp);
107      FourMomentum pKp  = boost2.transform(boost1.transform(Kp.momentum()));
108      FourMomentum pPhi = boost2.transform(boost1.transform(phi.momentum()));
109      LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(pPhi.betaVec());
110      pKp = boost3.transform(pKp);
111      double cK = axis2.dot(pKp.p3().unit());
112      _h[6]->fill(cK);
113      // omega decay
114      unsigned int ncount=0;
115      Particles pip,pim,pi0;
116      findChildren(omega,pim,pip,pi0,ncount);
117      if( ncount!=3 || !(pim.size()==1 && pip.size()==1 && pi0.size()==1)) vetoEvent;
118      // boost to omega/phi frame
119      FourMomentum ppip = boost2.transform(boost1.transform(pip[0].momentum()));
120      FourMomentum ppim = boost2.transform(boost1.transform(pim[0].momentum()));
121      FourMomentum pOmega = boost2.transform(boost1.transform(omega.momentum()));
122      LorentzTransform boost4 = LorentzTransform::mkFrameTransformFromBeta(pOmega.betaVec());
123      Vector3 axisZ = pOmega.p3().unit();
124      ppip = boost4.transform(ppip);
125      ppim = boost4.transform(ppim);
126      Vector3 norm = ppip.p3().cross(ppim.p3()).unit();
127      double cOmega = norm.dot(axisZ);
128      _h[4]->fill(cOmega);
129      // angle between planes
130      Vector3 Trans1 = pKp.p3() - cK*pKp.p3().mod()*axis2;
131      Vector3 Trans2 = norm     - cOmega*axisZ;
132      double chi = atan(Trans1.cross(Trans2).dot(axis2)/Trans1.dot(Trans2));
133      _h[8]->fill(abs(chi)/M_PI*180.);
134    }
135
136
137    /// Normalise histograms etc., after the run
138    void finalize() {
139      for(unsigned int ix=0;ix<9;++ix)
140	normalize(_h[ix],1.,false);
141    }
142
143    /// @}
144
145
146    /// @name Histograms
147    /// @{
148    Histo1DPtr _h[9];
149    /// @}
150
151
152  };
153
154
155  RIVET_DECLARE_PLUGIN(BESIII_2013_I1203841);
156
157}