Rivet analyses

title: BESIII_2019_I1692688

$e^+e^-$ mass distribution in $J/\psi\to\eta^\prime e^+e^-$

Experiment: BESIII (BEPC)

Inspire ID: 1692688

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 99 (2019) 1, 012013

Beams: * *

Beam energies: ANY

Run details: - Any process producing J/psi

$e^+e^-$ mass distribution in $J/\psi\to\eta^\prime e^+e^-$. Data read from plots in paper which are not efficiency corrected.

Source code:BESIII_2019_I1692688.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi -> eta' e+e- class BESIII_2019_I1692688 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2019_I1692688);


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

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


/// Perform the per-event analysis
void analyze(const Event& event) {
  // define the decay mode
  static const map<PdgId, unsigned int>& mode = {{PID::ETAPRIME, 1}, {11, 1}, {-11, 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& em = psi.decayProducts()[ix].at(11)[0];
    const Particle& ep = psi.decayProducts()[ix].at(-11)[0];
    double mee = (ep.momentum() + em.momentum()).mass();
    for (unsigned int ix = 0; ix < 2; ++ix) _h[ix]->fill(mee);
  }
}


/// 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_2019_I1692688);

} ```