Rivet analyses

title: BESII_2009_I819937

$J/\psi\to p \bar{p}\pi^0$

Experiment: BESII (BEPC)

Inspire ID: 819937

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 80 (2009) 052004

Beams: * *

Beam energies: ANY

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

Measurement of the mass distributions in the decay $J/\psi\to p \bar{p}\pi^0$. The data were read from the plots in the paper, but is corrected for detector efficiency.

Source code:BESII_2009_I819937.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi -> p pbar pi0 class BESII_2009_I819937 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESII_2009_I819937);


/// @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);
  book(_dalitz, "dalitz", 50, 1., 5., 50, 1., 5.);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{2212, 1}, {-2212, 1}, {111, 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& pi0 = psi.decayProducts()[ix].at(111);
    const Particles& pp = psi.decayProducts()[ix].at(2212);
    const Particles& pbar = psi.decayProducts()[ix].at(-2212);
    double mminus = (pbar[0].momentum() + pi0[0].momentum()).mass2();
    double mplus = (pp[0].momentum() + pi0[0].momentum()).mass2();
    _h[0]->fill(sqrt(mplus));
    _h[1]->fill(sqrt(mminus));
    _dalitz->fill(mplus, mminus);
  }
}


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

/// @}


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

};

RIVET_DECLARE_PLUGIN(BESII_2009_I819937);

} ```