Rivet analyses

Dalitz plot analysis of η_c → K⁺K⁻η^′, π⁺π⁻η and π⁺π⁻η^′

Experiment: BABAR (PEP-II)

Inspire ID: 1867843

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 104 (2021) 7, 072002

Beams: * *

Beam energies: ANY

Run details: - Any process producing eta_c (originally gamma gamma -> chi_c)

Measurement of the mass distributions in the decays η_c → K⁺K⁻η^′, π⁺π⁻η and π⁺π⁻η^′ by BaBar. 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:`BABAR_2021_I1867843.cc`

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

namespace Rivet {


  /// @brief eta_c Dalitz decays
  class BABAR_2021_I1867843 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2021_I1867843);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::pid== 441);
      declare(ufs, "UFS");
      DecayedParticles ETAC(ufs);
      ETAC.addStable(PID::PI0);
      ETAC.addStable(PID::K0S);
      ETAC.addStable(PID::ETA);
      ETAC.addStable(PID::ETAPRIME);
      declare(ETAC,"ETAC");
      // histograms
      book(_h_KK    ,1,1,1);
      book(_h_etaPK ,1,1,2);
      book(_h_pipi1 ,2,1,1);
      book(_h_etaPpi,2,1,2);
      book(_h_pipi2 ,3,1,1);
      book(_h_etapi ,3,1,2);
      book(_dalitz1, "dalitz1",50,2.,6.5,50,2.,6.5);
      book(_dalitz2, "dalitz2",50,0.,9. ,50,0.,9. );
      book(_dalitz3, "dalitz3",50,0.,8. ,50,0.,8. );
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId,unsigned int> & mode1  = { { 321,1}, {-321,1}, { 331,1}};
      static const map<PdgId,unsigned int> & mode2  = { { 211,1}, {-211,1}, { 331,1}};
      static const map<PdgId,unsigned int> & mode3  = { { 211,1}, {-211,1}, { 221,1}};
      DecayedParticles ETAC = apply<DecayedParticles>(event, "ETAC");
      // loop over particles
      for(unsigned int ix=0;ix<ETAC.decaying().size();++ix) {
    //K+ K- eta'
    if (ETAC.modeMatches(ix,3,mode1)&&
        ETAC.decaying()[ix].mass()>2.93 && ETAC.decaying()[ix].mass()<3.03) {
      const Particle & Kp   = ETAC.decayProducts()[ix].at( 321)[0];
      const Particle & Km   = ETAC.decayProducts()[ix].at(-321)[0];
      const Particle & etaP = ETAC.decayProducts()[ix].at( 331)[0];
      double mplus  = (Kp.momentum()+etaP.momentum()).mass2();
      double mminus = (Km.momentum()+etaP.momentum()).mass2();
      double mKK    = (Kp.momentum()+Km .momentum()).mass2();
      _h_KK   ->fill(sqrt(mKK));
      _h_etaPK->fill(sqrt(mplus));
      _h_etaPK->fill(sqrt(mminus));
      _dalitz1->fill(mplus,mminus);
    }
    // pi+ pi- eta'
    else if (ETAC.modeMatches(ix,3,mode2)&&
         ETAC.decaying()[ix].mass()>2.93 && ETAC.decaying()[ix].mass()<3.03) {
      const Particle & pip  = ETAC.decayProducts()[ix].at( 211)[0];
      const Particle & pim  = ETAC.decayProducts()[ix].at(-211)[0];
      const Particle & etaP = ETAC.decayProducts()[ix].at( 331)[0];
      double mplus  = (pip.momentum()+etaP.momentum()).mass2();
      double mminus = (pim.momentum()+etaP.momentum()).mass2();
      double mpipi    = (pip.momentum()+pim .momentum()).mass2();
      _h_pipi1 ->fill(sqrt(mpipi));
      _h_etaPpi->fill(sqrt(mplus));
      _h_etaPpi->fill(sqrt(mminus));
      _dalitz2->fill(mplus,mminus);
    }
    // pi+ pi- eta
    else if (ETAC.modeMatches(ix,3,mode3)&&
         ETAC.decaying()[ix].mass()>2.92 && ETAC.decaying()[ix].mass()<3.02) {
      const Particle & pip = ETAC.decayProducts()[ix].at( 211)[0];
      const Particle & pim = ETAC.decayProducts()[ix].at(-211)[0];
      const Particle & eta = ETAC.decayProducts()[ix].at( 221)[0];
      double mplus  = (pip.momentum()+eta.momentum()).mass2();
      double mminus = (pim.momentum()+eta.momentum()).mass2();
      double mpipi    = (pip.momentum()+pim .momentum()).mass2();
      _h_pipi2->fill(sqrt(mpipi));
      _h_etapi->fill(sqrt(mplus));
      _h_etapi->fill(sqrt(mminus));
      _dalitz3->fill(mplus,mminus);
    }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h_KK    );
      normalize(_h_etaPK );
      normalize(_h_pipi1 );
      normalize(_h_etaPpi);
      normalize(_h_pipi2 );
      normalize(_h_etapi );
      normalize(_dalitz1 );
      normalize(_dalitz2 );
      normalize(_dalitz3 );
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_KK,_h_etaPK;
    Histo1DPtr _h_pipi1,_h_etaPpi;
    Histo1DPtr _h_pipi2,_h_etapi;
    Histo2DPtr _dalitz1,_dalitz2,_dalitz3;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BABAR_2021_I1867843);

}

Rivet analyses

Dalitz plot analysis of ηc → K+K−η′, π+π−η and π+π−η′

Source code:BABAR_2021_I1867843.cc

Dalitz plot analysis of η_c → K⁺K⁻η^′, π⁺π⁻η and π⁺π⁻η^′

Source code:`BABAR_2021_I1867843.cc`