Rivet analyses

Dalitz plot analysis of J/ψ and ψ(2S) → π+π−η′

Experiment: BESIII (BEPC)

Inspire ID: 1621266

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 96 (2017) 11, 112012

Beams: * *

Beam energies: ANY

Run details: - Any process producing J/psi or psi(2S), originally e+e-

Measurement of the mass distributions in the decays J/ψ and ψ(2S) → π+π−η′ by BESIII. The data were read from the plots in the paper and therefore for some points the error bars are the size of the point. 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_2017_I1621266.cc

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

namespace Rivet {


  /// @brief J/psi$ and psi(2S) to pi+  pi- eta'
  class BESIII_2017_I1621266 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2017_I1621266);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::pid== 443 || Cuts::pid==100443);
      declare(ufs, "UFS");
      DecayedParticles PSI(ufs);
      PSI.addStable(PID::ETAPRIME);
      declare(PSI,"PSI");
      // histos
      book(_h_pipi [0],1,1,1);
      book(_h_pieta[0],1,1,2);
      book(_h_pipi [1],1,1,3);
      book(_h_pieta[1],1,1,4);
      book(_dalitz[0], "dalitz_Jpsi" ,50,1., 9.,50,1., 9.);
      book(_dalitz[1], "dalitz_psi2S",50,1.,14.,50,1.,14.);
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId,unsigned int> & mode   = { { 211,1},{-211,1}, {331,1}};
      DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
      // loop over particles
      for(unsigned int ix=0;ix<PSI.decaying().size();++ix) {
    if (!PSI.modeMatches(ix,3,mode)) continue;
    const Particle & pip = PSI.decayProducts()[ix].at( 211)[0];
    const Particle & pim = PSI.decayProducts()[ix].at(-211)[0];
    const Particle & eta = PSI.decayProducts()[ix].at( 331)[0];
    unsigned int iloc = PSI.decaying()[ix].pid()/100000;
    double mminus = (pim.momentum()+eta.momentum()).mass2();
    double mplus  = (pip.momentum()+eta.momentum()).mass2();
    double mneut  = (pip.momentum()+pim.momentum()).mass2();
    _h_pipi[iloc] ->fill(sqrt(mneut ));
    _h_pieta[iloc]->fill(sqrt(mplus ));
    //_h_pieta[iloc]->fill(sqrt(mminus));
    _dalitz[iloc]->fill(mplus,mminus);
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_pipi[2],_h_pieta[2];
    Histo2DPtr _dalitz[2];
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BESIII_2017_I1621266);

}