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BESIII_2018_I1703033

Dalitz plot analysis of $\omega\to\pi^+\pi^-\pi^0$
Experiment: BESIII (BEPC)
Inspire ID: 1703033
Status: VALIDATED NOHEPDATA
Authors:
  • Peter Richardson
References:
  • Phys.Rev.D 98 (2018) 11, 112007
Beams: * *
Beam energies: ANY
Run details:
  • Any process producing omega -> pi+pi-pi0

Measurement of kinematic distributions in the decay $\omega\to\pi^+\pi^-\pi^0$ by BESIII. The data were read from the plots in the paper and therefore for most points the error bars are the size of the point. It is also not clear that any resolution/acceptance effects have been unfolded.

Source code: BESIII_2018_I1703033.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/DecayedParticles.hh"

namespace Rivet {


  /// @brief omega -> pi+pi-pi0
  class BESIII_2018_I1703033 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1703033);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::pid== 223);
      declare(ufs, "UFS");
      DecayedParticles OMEGA(ufs);
      OMEGA.addStable(PID::PI0);
      declare(OMEGA,"OMEGA");
      // histograms
      book(_h_z  ,1,1,1);
      book(_h_phi,1,1,2);
      book(_h_cos,1,1,3);
      book(_h_ppi,1,1,4);
      book(_dalitz,"dalitz",50,-1,1,50,-1.1,0.9);
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId,unsigned int> & mode = { { 211,1}, {-211,1}, { 111,1}};
      static const std::complex<double> ii(0.,1.);
      DecayedParticles OMEGA = apply<DecayedParticles>(event, "OMEGA");
      // loop over particles
      for(unsigned int ix=0;ix<OMEGA.decaying().size();++ix) {
	// pi+ pi- pi0
	if (!OMEGA.modeMatches(ix,3,mode)) continue;
	// apply omega mass cut
	if(abs(OMEGA.decaying()[ix].mass()-0.78265)>0.04) continue;
	// decay products
	const Particle & pip = OMEGA.decayProducts()[ix].at( 211)[0];
	const Particle & pim = OMEGA.decayProducts()[ix].at(-211)[0];
	const Particle & pi0 = OMEGA.decayProducts()[ix].at( 111)[0];
	LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(OMEGA.decaying()[ix].momentum().betaVec());
	FourMomentum pp = boost.transform(pip.momentum());
	FourMomentum pm = boost.transform(pim.momentum());
	FourMomentum p0 = boost.transform(pi0.momentum());
	// variables from eqn 1 in paper (use version from Eqn 2.1 of 1010.3946)
	double Qc = OMEGA.decaying()[ix].mass()-pi0.mass()-pim.mass()-pip.mass();
	double x = sqrt(3.)*(pm.E()-pp.E())/Qc;
	double y = 3./Qc*(p0.E()-pi0.mass())-1.;
	_dalitz->fill(x,y);
	// plot arg and phase of variable
	std::complex<double> zz = x+ii*y;
	_h_z->fill(norm(zz));
	double phi = arg(zz);
	if(phi<0.) phi+=2.*M_PI;
	_h_phi->fill(phi);
	double ctheta = -pp.p3().unit().dot(p0.p3().unit());
	_h_cos->fill(ctheta);
	_h_ppi->fill(p0.p3().mod());
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h_z  );
      normalize(_h_phi);
      normalize(_h_cos);
      normalize(_h_ppi);
      normalize(_dalitz);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_z,_h_phi,_h_cos,_h_ppi;
    Histo2DPtr _dalitz;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BESIII_2018_I1703033);

}