Rivet analyses

title: BELLE_2020_I1785816

Dalitz decay of $D^0\to K^-\pi^+\eta$

Experiment: BELLE (KEKB)

Inspire ID: 1785816

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 102 (2020) 1, 012002

Beams: * *

Beam energies: ANY

Run details: - Any process producing D0 mesons

Measurement of the mass distributions in the decay $D^0\to K^-\pi^+\eta$ by BELLE. The data were read from the plots in the paper, and for many points the error bars are the size of the point. It is also not clear that any resolution effects have been unfolded.

Source code:BELLE_2020_I1785816.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D0 -> K- pi+ eta class BELLE_2020_I1785816 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2020_I1785816);


/// @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_Kpi, 1, 1, 1);
  book(_h_etapi, 1, 1, 2);
  book(_h_Keta, 1, 1, 3);
  book(_dalitz, "dalitz", 50, 0.3, 1.8, 50, 0.4, 1.9);
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{-321, 1}, {211, 1}, {221, 1}};
  static const map<PdgId, unsigned int>& modeCC = {{321, 1}, {-211, 1}, {221, 1}};
  DecayedParticles D0 = apply<DecayedParticles>(event, "D0");
  // loop over particles
  for (unsigned int ix = 0; ix < D0.decaying().size(); ++ix) {
    int sign = 1;
    if (D0.decaying()[ix].pid() > 0 && D0.modeMatches(ix, 3, mode)) {
      sign = 1;
    }
    else if (D0.decaying()[ix].pid() < 0 && D0.modeMatches(ix, 3, modeCC)) {
      sign = -1;
    }
    else
      continue;
    const Particles& eta = D0.decayProducts()[ix].at(221);
    const Particles& Km = D0.decayProducts()[ix].at(-sign * 321);
    const Particles& pip = D0.decayProducts()[ix].at(sign * 211);
    double metapi = (eta[0].momentum() + pip[0].momentum()).mass2();
    double metaK = (eta[0].momentum() + Km[0].momentum()).mass2();
    double mKpi = (Km[0].momentum() + pip[0].momentum()).mass2();
    _dalitz->fill(mKpi, metapi);
    _h_etapi->fill(metapi);
    _h_Keta->fill(metaK);
    _h_Kpi->fill(mKpi);
  }
}


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

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_Kpi, _h_etapi, _h_Keta;
Histo2DPtr _dalitz;
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2020_I1785816);

} ```