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CLEO_2009_I832707

Analysis of $\psi(2S)\to\gamma\chi_{c(1,2)}$ decays using $\chi_{c(1,2)}\to J/\psi\gamma$
Experiment: CLEO (CESR)
Inspire ID: 832707
Status: VALIDATED NOHEPDATA
Authors:
  • Peter Richardson
References:
  • Phys.Rev.D 80 (2009) 112003
Beams: e- e+
Beam energies: (1.8, 1.8) GeV
Run details:
  • e+e- > psi(2S)

Analysis of the angular distribution of the photons and leptons produced in $e^+e^-\to \psi(2S) \to \gamma\chi_{c(1,2)}$ followed by $\chi_{c(1,2)}\to\gamma J/\psi$ and $J/\psi\to\ell^+\ell^-$ Gives information about the decay and is useful for testing correlations in charmonium decays. N.B. the data was read from the figures in the paper and is not corrected and should only be used qualatively.

Source code: CLEO_2009_I832707.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/Beam.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief psi(2S) -> gamma chi_c1,2
  class CLEO_2009_I832707 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CLEO_2009_I832707);


    /// @name Analysis methods
    /// @{

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(Beam(), "Beams");
      declare(UnstableParticles(Cuts::pid==20443 || Cuts::pid==445), "UFS");
      declare(FinalState(), "FS");
      for(unsigned int ix=0;ix<2;++ix)
	book(_h[ix],1,1,1+ix);
    }

    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
      for( const Particle &child : p.children()) {
	if(child.children().empty()) {
	  nRes[child.pid()]-=1;
	  --ncount;
	}
	else
	  findChildren(child,nRes,ncount);
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // get the axis, direction of incoming electron
      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
      Vector3 axis;
      if(beams.first.pid()>0)
	axis = beams.first .momentum().p3().unit();
      else
	axis = beams.second.momentum().p3().unit();
      // types of final state particles
      const FinalState& fs = apply<FinalState>(event, "FS");
      map<long,int> nCount;
      int ntotal(0);
      for (const Particle& p :  fs.particles()) {
	nCount[p.pid()] += 1;
	++ntotal;
      }
      // loop over chi_c states
      Particle chi;
      bool matched = false;
      const UnstableParticles & ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& p :  ufs.particles()) {
       	if(p.children().empty()) continue;
       	map<long,int> nRes=nCount;
       	int ncount = ntotal;
       	findChildren(p,nRes,ncount);
	if(ncount==1) {
	  matched = true;
	  for(auto const & val : nRes) {
	    if(val.first==PID::PHOTON) {
	      if(val.second!=1) {
	      matched = false;
	      break;
	      }
	    }
	    else if(val.second!=0) {
	      matched = false;
	      break;
	    }
	  }
	  if(matched) {
	    chi=p;
	    break;
	  }
	}
      }
      if(!matched) vetoEvent;
      // have chi_c find psi2S 
      if(chi.parents().empty() || chi.children().size()!=2) vetoEvent;
      Particle psi2S = chi.parents()[0];
      if(psi2S.pid()!=100443 || psi2S.children().size()!=2) vetoEvent;
      // then the first photon
      Particle gamma1;
      if(psi2S.children()[0].pid()==PID::PHOTON)
	gamma1 = psi2S.children()[0];
      else if(psi2S.children()[1].pid()==PID::PHOTON)
	gamma1 = psi2S.children()[1];
      else
	vetoEvent;
      // then the J/psi and second photon
      Particle JPsi,gamma2;
      if(chi.children()[0].pid()==PID::PHOTON &&
	 chi.children()[1].pid()==443) {
	gamma2 = chi.children()[0];
	JPsi   = chi.children()[1];
      }
      else if(chi.children()[1].pid()==PID::PHOTON &&
	      chi.children()[0].pid()==443) {
	gamma2 = chi.children()[1];
	JPsi   = chi.children()[0];
      }
      else
	vetoEvent;
      // finally the leptons from J/psi decay
      if(JPsi.children().size()!=2) vetoEvent;
      if(JPsi.children()[0].pid()!=-JPsi.children()[1].pid()) vetoEvent;
      if(JPsi.children()[0].abspid()!=PID::EMINUS &&
	 JPsi.children()[0].abspid()!=PID::MUON) vetoEvent;
      Particle lm = JPsi.children()[0];
      Particle lp = JPsi.children()[1];
      if(lm.pid()<0) swap(lm,lp);
      // type chi state
      unsigned int ichi= chi.pid()==445 ? 1 : 0;
      // axis in the chi frame
      LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(chi.momentum().betaVec());
      FourMomentum pGamma2 = boost1.transform(gamma2.momentum());
      Vector3 axis1 = pGamma2.p3().unit();
      // cos thetaxs distributions
      FourMomentum pJpsi = boost1.transform(JPsi.momentum());
      FourMomentum plp   = boost1.transform(  lp.momentum());
      LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pJpsi.betaVec());
      Vector3 axis2 = boost2.transform(plp).p3().unit();
      Vector3 e2z = gamma2.momentum().p3().unit();
      _h[ichi]->fill(abs(e2z.dot(axis2)));
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for(unsigned int ix=0;ix<2;++ix) {
	normalize(_h[ix]);
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[2];
    /// @}


  };


  RIVET_DECLARE_PLUGIN(CLEO_2009_I832707);

}