Rivet analyses

title: BESIII_2019_I1731057

Dalitz plot analysis of $J/\psi\to K^+K^-\pi^0$

Experiment: BESIII (BEPC)

Inspire ID: 1731057

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 100 (2019) 3, 032004

Beams: * *

Beam energies: ANY

Run details: - Any process producing J/psi, originally e+e-

Measurement of the mass distributions in the decays $J/\psi\to K^+K^-\pi^0$ by BESIII. The data were read from the plots in the paper and therefore for most points the error bars are the size of the point. It is also not clear that any resolution/acceptance effects have been unfolded.

Source code:BESIII_2019_I1731057.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi -> K+K-pi0 class BESIII_2019_I1731057 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2019_I1731057);


/// @name Analysis methods
/// @{

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::pid == 443);
  declare(ufs, "UFS");
  DecayedParticles PSI(ufs);
  PSI.addStable(PID::PI0);
  declare(PSI, "PSI");
  // histos
  for (unsigned int ix = 0; ix < 2; ++ix) {
    book(_h_KpKm[ix], 1 + ix, 1, 1);
    book(_h_Kppi0[ix], 1 + ix, 1, 2);
  }
  book(_dalitz, "dalitz", 50, 0., 7., 50, 0.0, 7.);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{321, 1}, {-321, 1}, {111, 1}};
  DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
  // loop over particles
  for (unsigned int ix = 0; ix < PSI.decaying().size(); ++ix) {
    if (!PSI.modeMatches(ix, 3, mode)) continue;
    const Particle& Kp = PSI.decayProducts()[ix].at(321)[0];
    const Particle& Km = PSI.decayProducts()[ix].at(-321)[0];
    const Particle& pi0 = PSI.decayProducts()[ix].at(111)[0];
    double mminus = (Km.momentum() + pi0.momentum()).mass2();
    double mplus = (Kp.momentum() + pi0.momentum()).mass2();
    double mneut = (Kp.momentum() + Km.momentum()).mass2();
    _dalitz->fill(mplus, mminus);
    mplus = sqrt(mplus);
    mminus = sqrt(mminus);
    mneut = sqrt(mneut);
    _h_KpKm[0]->fill(mneut);
    _h_Kppi0[0]->fill(mplus);
    _h_Kppi0[0]->fill(mminus);
    if (mplus > 1.05 && mminus > 1.05) {
      _h_KpKm[1]->fill(mneut);
      _h_Kppi0[1]->fill(mplus);
      _h_Kppi0[1]->fill(mminus);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 2; ++ix) {
    normalize(_h_KpKm[ix], 1., false);
    normalize(_h_Kppi0[ix], 1., false);
  }
  normalize(_dalitz);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_KpKm[2], _h_Kppi0[2];
Histo2DPtr _dalitz;
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2019_I1731057);

} ```