Rivet analyses

Dalitz decay of Ds+ → π+π0η

Experiment: BESIII (BEPC)

Inspire ID: 1724547

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 123 (2019) 11, 112001

Beams: * *

Beam energies: ANY

Run details: - Any process producing D_s+ mesons

Measurement of the mass distributions in the decay Ds+ → π+π0η by BES. The data were read from the plots in the paper and therefore for some points the error bars are the size of the point. It is also not clear that any resolution effects have been unfolded.

Source code:BESIII_2019_I1724547.cc

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

namespace Rivet {


  /// @brief D_s+ -> pi+ pi0 eta
  class BESIII_2019_I1724547 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2019_I1724547);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid==431);
      declare(ufs, "UFS");
      DecayedParticles DS(ufs);
      DS.addStable(PID::PI0);
      DS.addStable(PID::K0S);
      DS.addStable(PID::ETA);
      declare(DS,"DS");
      // histograms
      book(_h_pipi, 1,1,1);
      book(_h_etapip[0],1,1,2);
      book(_h_etapip[1],1,1,4);
      book(_h_etapi0[0],1,1,3);
      book(_h_etapi0[1],1,1,5);
      book(_dalitz, "dalitz",50,0.3,3.4,50,0.3,3.4);
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId,unsigned int> & mode   = { { 211,1},{ 111,1}, {221,1}};
      static const map<PdgId,unsigned int> & modeCC = { {-211,1},{ 111,1}, {221,1}};
      DecayedParticles DS = apply<DecayedParticles>(event, "DS");
      // loop over particles
      for(unsigned int ix=0;ix<DS.decaying().size();++ix) {
    int sign = 1;
    if (DS.decaying()[ix].pid()>0 && DS.modeMatches(ix,3,mode)) {
      sign=1;
    }
    else if  (DS.decaying()[ix].pid()<0 && DS.modeMatches(ix,3,modeCC)) {
      sign=-1;
    }
    else
      continue;
    const Particle & eta = DS.decayProducts()[ix].at(      221)[0];
    const Particle & pi0 = DS.decayProducts()[ix].at(      111)[0];
    const Particle & pip = DS.decayProducts()[ix].at( sign*211)[0];
    double mplus = (eta.momentum()+pip.momentum()).mass2();
    double mzero = (eta.momentum()+pi0.momentum()).mass2();
    double mpipi = (pip.momentum()+pi0.momentum()).mass2();
    _dalitz->fill(mplus,mzero);
    _h_pipi     ->fill(sqrt(mpipi));
    _h_etapip[0]->fill(sqrt(mplus));
    _h_etapi0[0]->fill(sqrt(mzero));
    if(mpipi>1.) {
      _h_etapip[1]->fill(sqrt(mplus));
      _h_etapi0[1]->fill(sqrt(mzero));
    }
      }
    }

    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h_pipi     );
      normalize(_h_etapip[0]);
      normalize(_h_etapip[1]);
      normalize(_h_etapi0[0]);
      normalize(_h_etapi0[1]);
      normalize(_dalitz     );
    }

    /// @}
    /// @name Histograms
    /// @{
    Histo1DPtr _h_pipi, _h_etapip[2],_h_etapi0[2];
    Histo2DPtr _dalitz;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BESIII_2019_I1724547);

}