Rivet analyses

title: BESIII_2016_I1484158

$\eta\pi^0$ mass distribution in $J/\psi\to\gamma\eta\pi^0$

Experiment: BESIII (BEPC)

Inspire ID: 1484158

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 94 (2016) 7, 072005

Beams: * *

Beam energies: ANY

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

Measurement of the $\eta\pi^0$ mass distribution in $J/\psi\to\gamma\eta\pi^0$ decays. The data were read from the plots in the paper and the backgrounds given subtracted, although acceptance/efficiency may not be corrected.

Source code:BESIII_2016_I1484158.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi -> gamma eta pi0 class BESIII_2016_I1484158 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2016_I1484158);


/// @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::ETA);
  declare(psi, "psi");
  //histograms
  book(_h, 1, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{221, 1}, {111, 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, 3, mode)) continue;
    const Particle& eta = psi.decayProducts()[ix].at(221)[0];
    const Particle& pi0 = psi.decayProducts()[ix].at(111)[0];
    _h->fill((eta.momentum() + pi0.momentum()).mass());
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h, 1., false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h;
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2016_I1484158);

} ```