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BESIII_2012_I1088606

Mass distributions in $J/\psi$ and $\psi(2S)$ to $\pi^+\pi^-\pi^0$
Experiment: BESIII (BEPC)
Inspire ID: 1088606
Status: VALIDATED NOHEPDATA
Authors:
  • Peter Richardson
References:
  • Phys.Lett.B 710 (2012) 594-599
Beams: * *
Beam energies: ANY
Run details:
  • Any process producing J/psi or psi(2S), originally e+e-

Measurement of the $\pi\pi$ mass distribution in the decays $J/\psi$ and $\psi(2S)$ to $\pi^+\pi^-\pi^0$ be BES. N.B. data read from plots and may not be corrected.

Source code: BESIII_2012_I1088606.cc 
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/DecayedParticles.hh"

namespace Rivet {


  /// @brief J/psi and psi(2S) -> pi+pi-pi0
  class BESIII_2012_I1088606 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2012_I1088606);


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

    /// Book histograms and initialise projections before the run
    void init() {
      UnstableParticles ufs = UnstableParticles(Cuts::pid==443 or Cuts::pid==100443);
      declare(ufs, "UFS");
      DecayedParticles psi(ufs);
      psi.addStable(PID::PI0);
      psi.addStable(PID::K0S);
      psi.addStable(PID::ETA);
      psi.addStable(PID::ETAPRIME);
      declare(psi, "psi");
      book(_h_pipi[0],1,1,1);
      book(_h_pipi[1],1,1,2);
      book(_dalitz[0], "dalitz_Jpsi" ,50,0.,9. ,50,0.0, 9.);
      book(_dalitz[1], "dalitz_psi2S",50,0.,14.,50,0.0,14.);
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId,unsigned int> & mode   = { { 211,1}, {-211,1}, { 111,1} };
      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 Particles & pi0 = psi.decayProducts()[ix].at( 111);
	const Particles & pip = psi.decayProducts()[ix].at( 211);
	const Particles & pim = psi.decayProducts()[ix].at(-211);
	double mminus = (pim[0].momentum()+pi0[0].momentum()).mass2();
	double mplus  = (pip[0].momentum()+pi0[0].momentum()).mass2();
	double mneut  = (pip[0].momentum()+pim[0].momentum()).mass2();
	unsigned int iloc = psi.decaying()[ix].pid()/100000;
	_h_pipi[iloc]->fill(sqrt(mneut ));
	_h_pipi[iloc]->fill(sqrt(mplus ));
	_h_pipi[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(_dalitz[ix]);
      }
    }

    /// @}


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


  };


  RIVET_DECLARE_PLUGIN(BESIII_2012_I1088606);

}