Rivet analyses

π0η mass distribution in D0 → π0ηη

Experiment: BESIII (BEPC)

Inspire ID: 1662665

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Lett.B 781 (2018) 368-375

Beams: * *

Beam energies: ANY

Run details: - Any process producing D0 mesons

Measurement of the π0η mass distribution in D0 → π0ηη by BES. The data were read from the plots in the paper. It is also not clear that any resolution effects have been unfolded.

Source code:BESIII_2018_I1662665.cc

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

namespace Rivet {


  /// @brief D0 -> eta eta pi0
  class BESIII_2018_I1662665 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1662665);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 421);
      declare(ufs, "UFS");
      DecayedParticles D0(ufs);
      D0.addStable(PID::PI0);
      D0.addStable(PID::K0S);
      D0.addStable(PID::ETA);
      D0.addStable(PID::ETAPRIME);
      declare(D0, "D0");
      // histograms
      book(_h_pieta, 1, 1, 1);
      book(_dalitz, "dalitz", 50., 0.4, 1.6, 50, 0.4, 1.8);
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // define the decay mode
      static const map<PdgId, unsigned int>& mode = {{221, 2}, {111, 1}};
      DecayedParticles D0 = apply<DecayedParticles>(event, "D0");
      // loop over particles
      for (unsigned int ix = 0; ix < D0.decaying().size(); ++ix) {
        if (!D0.modeMatches(ix, 3, mode)) continue;
        const Particles& eta = D0.decayProducts()[ix].at(221);
        const Particles& pi0 = D0.decayProducts()[ix].at(111);
        double m1 = (eta[0].momentum() + pi0[0].momentum()).mass2();
        double m2 = (eta[1].momentum() + pi0[0].momentum()).mass2();
        if (m1 > m2) swap(m1, m2);
        _dalitz->fill(m1, m2);
        _h_pieta->fill(sqrt(m1));
        _h_pieta->fill(sqrt(m2));
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_pieta;
    Histo2DPtr _dalitz;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2018_I1662665);

}