Rivet analyses

Mass and angluar distributions in J/ψ → γηη^′

Experiment: BESIII (BEPC)

Inspire ID: 2135117

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 106 (2022) 7, 072012

Beams: * *

Beam energies: ANY

Run details: - Any process producing J/psi, originally e+e-

Measurement of mass and angluar distributions in J/ψ → γηη^′ by BESIII. The background subtracted data were read from the plots in the paper.

Source code:`BESIII_2022_I2135117.cc`

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/DecayedParticles.hh"

namespace Rivet {


  /// @brief J/psi -> gamma eta eta'
  class BESIII_2022_I2135117 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2135117);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid==443);
      declare(ufs, "UFS");
      DecayedParticles PSI(ufs);
      PSI.addStable(PID::ETA);
      PSI.addStable(PID::ETAPRIME);
      declare(PSI, "PSI");
      // histos
      for(unsigned int ix=0;ix<3;++ix) {
    book(_h_angle[ix],2,1,1+ix);
    book(_h_mass [ix],1,1,1+ix);
      }
      book(_h_angle[3],1,1,4);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // find the J/psi decays
      static const map<PdgId,unsigned int> & mode = { { 22,1},{ 221,1},{ 331,1}};
      DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
      for(unsigned int ix=0;ix<PSI.decaying().size();++ix) {
    if(!PSI.modeMatches(ix,3,mode)) continue;
    const Particle  & eta  = PSI.decayProducts()[ix].at(221)[0];
    const Particle  & etap = PSI.decayProducts()[ix].at(331)[0];
    const Particle  & gam  = PSI.decayProducts()[ix].at( 22)[0];
    double mEE = (eta.momentum()+etap.momentum()).mass();
    double mEG = (gam.momentum()+eta .momentum()).mass();
    if(abs(mEG-1.019461)<0.04) continue;
    _h_mass[0]->fill(mEE);
    _h_mass[1]->fill(mEG);
    _h_mass[2]->fill((gam.momentum()+etap.momentum()).mass());
    // angles
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(PSI.decaying()[0].momentum().betaVec());
    FourMomentum pGamma = boost1.transform(gam.momentum());
    FourMomentum pEE    = boost1.transform(eta.momentum()+etap.momentum());
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pEE.betaVec());
    Vector3 axis2 = boost2.transform(boost1.transform(eta.momentum())).p3().unit();
    double cTheta = pGamma.p3().unit().dot(axis2);
    _h_angle[3]->fill(cTheta);
    if( mEE>1.5 && mEE<1.7)
      _h_angle[0]->fill(cTheta);
    else if(mEE>1.7 && mEE<2.)
      _h_angle[1]->fill(cTheta);
    else if(mEE>2. && mEE<3.2)
      _h_angle[2]->fill(cTheta);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for(unsigned int ix=0;ix<4;++ix) {
    normalize(_h_angle[ix],1.,false);
    if(ix<3) normalize(_h_mass[ix],1.,false);
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_mass[3],_h_angle[4];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2022_I2135117);

}

Rivet analyses

Mass and angluar distributions in J/ψ → γηη′

Source code:BESIII_2022_I2135117.cc

Mass and angluar distributions in J/ψ → γηη^′

Source code:`BESIII_2022_I2135117.cc`