Rivet analyses

title: BESIII_2022_I2016785

Radiative $J/\psi\to\gamma \eta^\prime\eta^\prime$

Experiment: BESIII (BEPC)

Inspire ID: 2016785

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 105 (2022) 7, 072002

Beams: * *

Beam energies: ANY

Run details: none listed

Measurement of the mass distributions in the decay $J/\psi\to\gamma \eta^\prime\eta^\prime$. 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_2022_I2016785.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi -> gamma eta' eta' class BESIII_2022_I2016785 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2016785);


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

/// Book histograms and initialise projections before the run
void init() {
  UnstableParticles ufs = UnstableParticles(Cuts::pid == 443);
  declare(ufs, "UFS");
  DecayedParticles psi(ufs);
  psi.addStable(PID::PI0);
  psi.addStable(PID::K0S);
  psi.addStable(PID::ETA);
  psi.addStable(PID::ETAPRIME);
  declare(psi, "psi");
  for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], 1, 1, 1 + ix);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{331, 2}, {22, 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 Particles& eta = psi.decayProducts()[ix].at(331);
    const Particle& gamma = psi.decayProducts()[ix].at(22)[0];
    _h[0]->fill((eta[0].momentum() + eta[1].momentum()).mass());
    for (unsigned int ix = 0; ix < 2; ++ix) _h[1]->fill((gamma.momentum() + eta[ix].momentum()).mass());
  }
}


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

/// @}


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

};

RIVET_DECLARE_PLUGIN(BESIII_2022_I2016785);

} ```