Rivet analyses

title: BESII_2006_I650381

$J/\psi\to p \bar{n}\pi^-$ and $n\bar{p}\pi^+$

Experiment: BESII (BEPC)

Inspire ID: 650381

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 97 (2006) 062001

Beams: * *

Beam energies: ANY

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

Measurement of the mass distributions in the decays $J/\psi\to p \bar{n}\pi^-$ and $n\bar{p}\pi^+$. The data were read from the plots in the paper and may not be corrected for efficiency or background.

Source code:BESII_2006_I650381.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi -> p nbar pi+ + c.c class BESII_2006_I650381 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESII_2006_I650381);


/// @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[ix], "dalitz_" + toString(ix + 1), 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}, {-2112, 1}, {-211, 1}};
  static const map<PdgId, unsigned int>& modeCC = {{-2212, 1}, {2112, 1}, {211, 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)) {
      const Particle& pim = psi.decayProducts()[ix].at(-211)[0];
      const Particle& pp = psi.decayProducts()[ix].at(2212)[0];
      const Particle& nbar = psi.decayProducts()[ix].at(-2112)[0];
      double mminus = (pp.momentum() + pim.momentum()).mass2();
      double mplus = (nbar.momentum() + pim.momentum()).mass2();
      _h[0]->fill(sqrt(mminus));
      _dalitz[0]->fill(mminus, mplus);
    }
    else if (psi.modeMatches(ix, 3, modeCC)) {
      const Particle& pip = psi.decayProducts()[ix].at(211)[0];
      const Particle& nn = psi.decayProducts()[ix].at(2112)[0];
      const Particle& pbar = psi.decayProducts()[ix].at(-2212)[0];
      double mminus = (pbar.momentum() + pip.momentum()).mass2();
      double mplus = (nn.momentum() + pip.momentum()).mass2();
      _h[1]->fill(sqrt(mminus));
      _dalitz[1]->fill(mminus, mplus);
    }
  }
}


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

/// @}


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

};

RIVET_DECLARE_PLUGIN(BESII_2006_I650381);

} ```