Rivet analyses

Dalitz decay of Ds+ → π+π0η′

Experiment: BESIII (BEPC)

Inspire ID: 2030993

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2202.04232

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. It is also not clear that any resolution effects have been unfolded.

Source code:BESIII_2022_I2030993.cc

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

namespace Rivet {


  /// @brief D_s+ -> pi+ pi0 eta'
  class BESIII_2022_I2030993 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2030993);


    /// @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::ETAPRIME);
      declare(DS, "DS");
      // histograms
      book(_h_etapip, 1, 1, 1);
      book(_h_etapi0, 1, 1, 2);
      book(_h_pipi, 1, 1, 3);
      book(_dalitz, "dalitz", 50, 0., 1.1, 50, 1, 3.5);
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{211, 1}, {111, 1}, {331, 1}};
      static const map<PdgId, unsigned int>& modeCC = {{-211, 1}, {111, 1}, {331, 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& pip = DS.decayProducts()[ix].at(sign * 211)[0];
        const Particle& pi0 = DS.decayProducts()[ix].at(111)[0];
        const Particle& eta = DS.decayProducts()[ix].at(331)[0];
        double mplus = (eta.momentum() + pip.momentum()).mass2();
        double mzero = (eta.momentum() + pi0.momentum()).mass2();
        double mpipi = (pip.momentum() + pi0.momentum()).mass2();
        _dalitz->fill(mpipi, mplus);
        _h_pipi->fill(sqrt(mpipi));
        _h_etapip->fill(sqrt(mplus));
        _h_etapi0->fill(sqrt(mzero));
      }
    }


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

    /// @}


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


  RIVET_DECLARE_PLUGIN(BESIII_2022_I2030993);

}