Rivet analyses

title: BESIII_2019_I1709205

$J/\psi$ and $\psi(2S)\to p \bar{p}\eta^\prime$

Experiment: BESIII (BEPC)

Inspire ID: 1709205

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 99 (2019) 3, 032006

Beams: * *

Beam energies: ANY

Run details: - Any process producing J/psi or psi(2S) originally e+e-

Measurement of the mass distributions in the decay $J/\psi$ or $\psi(2S)\to p \bar{p}\eta^\prime$. 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_2019_I1709205.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi psi(2S) -> p pbar eta' class BESIII_2019_I1709205 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2019_I1709205);


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

/// Book histograms and initialise projections before the run
void init() {
  UnstableParticles ufs = UnstableParticles(Cuts::pid == 443 or Cuts::pid == 100443);
  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 < 6; ++iy) {
      book(_h[ix][iy], 1 + ix, 1, 1 + iy);
    }
  }
  book(_dalitz[0], "dalitz_1", 50, 3., 8., 50, 3., 8.);
  book(_dalitz[1], "dalitz_2", 50, 3.5, 5., 50, 3.5, 5.);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{2212, 1}, {-2212, 1}, {331, 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& etap = psi.decayProducts()[ix].at(331);
    const Particles& pp = psi.decayProducts()[ix].at(2212);
    const Particles& pbar = psi.decayProducts()[ix].at(-2212);
    double mminus = (pbar[0].momentum() + etap[0].momentum()).mass2();
    double mplus = (pp[0].momentum() + etap[0].momentum()).mass2();
    double mneut = (pp[0].momentum() + pbar[0].momentum()).mass2();
    unsigned int iloc = psi.decaying()[ix].pid() == 443 ? 1 : 0;
    for (unsigned int ix = 0; ix < 4; ix += 3) {
      _h[iloc][ix + 2]->fill(sqrt(mneut));
      _h[iloc][ix + 0]->fill(sqrt(mplus));
      _h[iloc][ix + 1]->fill(sqrt(mminus));
    }
    _dalitz[iloc]->fill(mplus, mminus);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 2; ++ix) {
    normalize(_dalitz[ix]);
    for (unsigned int iy = 0; iy < 6; ++iy) {
      normalize(_h[ix][iy]);
    }
  }
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[2][6];
Histo2DPtr _dalitz[2];
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2019_I1709205);

} ```