Rivet analyses

title: BESIII_2018_I1662665

$\pi^0\eta$ mass distribution in $D^0\to\pi^0\eta\eta$

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 $\pi^0\eta$ mass distribution in $D^0\to\pi^0\eta\eta$ 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++ // -- 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);

} ```