Rivet analyses

title: BESIII_2022_I2018236

Radiative $J/\psi\to\gamma \eta^\prime\pi^+\pi^-$ decay

Experiment: BESIII (BEPC)

Inspire ID: 2018236

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 129 (2022) 4, 042001

Beams: * *

Beam energies: ANY

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

Measurement of the hadronic mass distribution in the decay $J/\psi\to\gamma \eta^\prime\pi^+\pi^-$. 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_I2018236.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi -> gamma eta' pi+pi- class BESIII_2022_I2018236 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2018236);


/// @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)
    for (unsigned int iy = 0; iy < 2; ++iy)
      for (unsigned int iz = 1; iz < 2; ++iz) book(_h[ix][iy][iz], 1 + ix, 1 + iy, 1 + iz);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{211, 1}, {-211, 1}, {331, 1}, {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, 4, mode)) continue;
    const Particle& eta = psi.decayProducts()[ix].at(331)[0];
    const Particle& pip = psi.decayProducts()[ix].at(211)[0];
    const Particle& pim = psi.decayProducts()[ix].at(-211)[0];
    double m1 = (pip.momentum() + pim.momentum() + eta.momentum()).mass();
    double m2 = (pip.momentum() + pim.momentum()).mass();
    for (unsigned int ix = 0; ix < 2; ++ix) {
      _h[0][ix][1]->fill(m1);
      _h[1][ix][1]->fill(m2);
    }
  }
}


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

/// @}


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

};

RIVET_DECLARE_PLUGIN(BESIII_2022_I2018236);

} ```