Rivet analyses

title: BELLE_2021_I1867474

Mass distributions in $D^0\to\pi^+\pi^-\eta$ and $D^0\to K^+K^-\eta$

Experiment: BELLE (KEKB)

Inspire ID: 1867474

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - JHEP 09 (2021) 075

Beams: * *

Beam energies: ANY

Run details: - Any process producing D0 mesons

Measurement of the mass distributions in the decays $D^0\to\pi^+\pi^-\eta$ and $D^0\to K^+K^-\eta$ 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_2021_I1867474.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D0 -> pi+pi-eta, K+K-eta class BELLE_2021_I1867474 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2021_I1867474);


/// @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) {
  DecayedParticles D0 = apply<DecayedParticles>(event, "D0");
  // loop over particles
  for (unsigned int ix = 0; ix < D0.decaying().size(); ++ix) {
    unsigned int imode = 0;
    if (D0.modeMatches(ix, 3, mode1))
      imode = 0;
    else if (D0.modeMatches(ix, 3, mode2))
      imode = 1;
    else
      continue;
    int sign = D0.decaying()[ix].pid() / D0.decaying()[ix].abspid();
    int im = 211 + imode * 110;
    const Particle& eta = D0.decayProducts()[ix].at(221)[0];
    const Particle& pim = D0.decayProducts()[ix].at(-sign * im)[0];
    const Particle& pip = D0.decayProducts()[ix].at(sign * im)[0];
    _h[imode][0]->fill((pip.mom() + pim.mom()).mass2());
    _h[imode][1]->fill((pim.mom() + eta.mom()).mass2());
    _h[imode][2]->fill((pip.mom() + eta.mom()).mass2());
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 2; ++ix) {
    normalize(_h[ix], 1.0, false);
  }
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[2][3];
const map<PdgId, unsigned int> mode1 = {{211, 1}, {-211, 1}, {221, 1}};
const map<PdgId, unsigned int> mode2 = {{321, 1}, {-321, 1}, {221, 1}};
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2021_I1867474);

} ```