Rivet analyses

Dalitz plot analysis of ψ(2S) → K+K−η

Experiment: BESIII (BEPC)

Inspire ID: 1771616

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 101 (2020) 3, 032008

Beams: * *

Beam energies: ANY

Run details: - Any process producing psi(2S) originally e+e-

Measurement of the mass distributions in the decay ψ(2S) → K+K−η. The data were read from the plots in the paper. Also the sideband background from the plots has been subtracted. It is also not clear that any resolution effects have been unfolded.

Source code:BESIII_2020_I1771616.cc

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

namespace Rivet {


  /// @brief psi(2S) -> K+K- eta
  class BESIII_2020_I1771616 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1771616);


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

    /// Book histograms and initialise projections before the run
    void init() {
      UnstableParticles ufs = UnstableParticles(Cuts::pid==100443);
      declare(ufs, "UFS");
      DecayedParticles psi2S(ufs);
      psi2S.addStable(PID::PI0);
      psi2S.addStable(PID::K0S);
      psi2S.addStable(PID::ETA);
      psi2S.addStable(PID::ETAPRIME);
      declare(psi2S, "psi2S");
      for(unsigned int ix=0;ix<3;++ix)
    book(_h[ix],1,1,1+ix);
      book(_dalitz, "dalitz",50,0.,11.,50,0.0,11.);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId,unsigned int> & mode   = { { 321,1}, {-321,1}, { 221,1} };
      DecayedParticles psi2S = apply<DecayedParticles>(event, "psi2S");
      // loop over particles
      for(unsigned int ix=0;ix<psi2S.decaying().size();++ix) {
    if(!psi2S.modeMatches(ix,3,mode)) continue;
    const Particles & eta = psi2S.decayProducts()[ix].at( 221);
    const Particles & Kp  = psi2S.decayProducts()[ix].at( 321);
    const Particles & Km  = psi2S.decayProducts()[ix].at(-321);
    double mminus = (Km[0].momentum()+eta[0].momentum()).mass2();
    double mplus  = (Kp[0].momentum()+eta[0].momentum()).mass2();
    double mneut  = (Kp[0].momentum()+Km [0].momentum()).mass2();
    _h[0]->fill(sqrt(mneut ));
    _h[1]->fill(sqrt(mplus ));
    _h[2]->fill(sqrt(mminus));
    _dalitz->fill(mplus,mminus);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for(unsigned int ix=0;ix<3;++ix)
    normalize(_h[ix]);
      normalize(_dalitz);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[3];
    Histo2DPtr _dalitz;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BESIII_2020_I1771616);

}