Rivet analyses

Dalitz plot analysis of Ds+ → π+π0π0

Experiment: BESIII (BEPC)

Inspire ID: 1929365

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - JHEP 01 (2022) 052

Beams: * *

Beam energies: ANY

Run details: - Any process producting D_s mesons, originally e+e-

Measurement of the mass distributions in the decay Ds+ → π+π0π0. The data were read from the plots in the paper. Resolution/acceptance effects have been not unfolded and given the agreement with the model in the paper this analysis should only be used for qualitative studies.

Source code:BESIII_2021_I1929365.cc

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

namespace Rivet {


  /// @brief D_s+ -> pi+ pi0 pi0
  class BESIII_2021_I1929365 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1929365);


    /// @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);
      declare(DS, "DS");
      // histos
      book(_h_pi0pi0, 1, 1, 1);
      book(_h_pippi0, 1, 1, 2);
      book(_dalitz, "dalitz", 50, 0., 3.5, 50, 0., 3.5);
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{211, 1}, {111, 2}};
      static const map<PdgId, unsigned int>& modeCC = {{-211, 1}, {111, 2}};
      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 Particles& pi0 = DS.decayProducts()[ix].at(111);
        const Particle& pip = DS.decayProducts()[ix].at(sign * 211)[0];
        double mp1 = (pip.momentum() + pi0[0].momentum()).mass2();
        double mp2 = (pip.momentum() + pi0[1].momentum()).mass2();
        double m0 = (pi0[0].momentum() + pi0[1].momentum()).mass();
        _dalitz->fill(mp1, mp2);
        _dalitz->fill(mp2, mp1);
        // K_S0 veto
        if (m0 > 0.458 && m0 < 0.520) continue;
        _h_pippi0->fill(sqrt(mp1));
        _h_pippi0->fill(sqrt(mp2));
        _h_pi0pi0->fill(m0);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h_pi0pi0);
      normalize(_h_pippi0);
      normalize(_dalitz);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_pi0pi0, _h_pippi0;
    Histo2DPtr _dalitz;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2021_I1929365);

}