Rivet analyses

Dalitz plot analysis of D0 → KS, L0π+π−

Experiment: BESIII (BEPC)

Inspire ID: 2615968

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2212.09048

Beams: * *

Beam energies: ANY

Run details: - Any process producing D0 mesons

Measurement of Kinematic distributions in the decay D0 → KS0π+π− by BESIII. The data were read from the plots in the paper and resolution/acceptance effects may not have been unfolded.

Source code:BESIII_2022_I2615968.cc

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

namespace Rivet {


  /// @brief D0 -> KS0, KL0 pi+ pi-
  class BESIII_2022_I2615968 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2615968);


    /// @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
      for (unsigned int ix = 0; ix < 2; ++ix)
        for (unsigned int iy = 0; iy < 3; ++iy) book(_h[ix][iy], 1 + ix, 1, 1 + iy);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // // define the decay mode
      static const map<PdgId, unsigned int>& mode1 = {{310, 1}, {211, 1}, {-211, 1}};
      static const map<PdgId, unsigned int>& mode2 = {{130, 1}, {211, 1}, {-211, 1}};
      DecayedParticles D0 = apply<DecayedParticles>(event, "D0");
      // loop over particles
      for (unsigned int ix = 0; ix < D0.decaying().size(); ++ix) {
        int sign = D0.decaying()[ix].pid() / 421;
        int imode = 0;
        // KS0 pi+pi-
        if (D0.modeMatches(ix, 3, mode1))
          imode = 0;
        else if (D0.modeMatches(ix, 3, mode2))
          imode = 1;
        else
          continue;
        const Particle& pip = D0.decayProducts()[ix].at(sign * 211)[0];
        const Particle& pim = D0.decayProducts()[ix].at(-sign * 211)[0];
        const Particle& K0 = D0.decayProducts()[ix].at(imode == 0 ? 310 : 130)[0];
        double mminus = (pim.momentum() + K0.momentum()).mass2();
        double mplus = (pip.momentum() + K0.momentum()).mass2();
        double mpipi = (pip.momentum() + pim.momentum()).mass2();
        _h[imode][0]->fill(mplus);
        _h[imode][1]->fill(mminus);
        _h[imode][2]->fill(mpipi);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 2; ++ix)
        for (unsigned int iy = 0; iy < 3; ++iy) normalize(_h[ix][iy], 1., false);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[2][3];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2022_I2615968);

}