Rivet analyses

title: BESIII_2012_I1088606

Mass distributions in $J/\psi$ and $\psi(2S)$ to $\pi^+\pi^-\pi^0$

Experiment: BESIII (BEPC)

Inspire ID: 1088606

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Lett.B 710 (2012) 594-599

Beams: * *

Beam energies: ANY

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

Measurement of the $\pi\pi$ mass distribution in the decays $J/\psi$ and $\psi(2S)$ to $\pi^+\pi^-\pi^0$ be BES. N.B. data read from plots and may not be corrected.

Source code:BESIII_2012_I1088606.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi and psi(2S) -> pi+pi-pi0 class BESIII_2012_I1088606 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2012_I1088606);


/// @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");
  book(_h_pipi[0], 1, 1, 1);
  book(_h_pipi[1], 1, 1, 2);
  book(_dalitz[0], "dalitz_Jpsi", 50, 0., 9., 50, 0.0, 9.);
  book(_dalitz[1], "dalitz_psi2S", 50, 0., 14., 50, 0.0, 14.);
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  static const map<PdgId, unsigned int>& mode = {{211, 1}, {-211, 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& pip = psi.decayProducts()[ix].at(211);
    const Particles& pim = psi.decayProducts()[ix].at(-211);
    double mminus = (pim[0].momentum() + pi0[0].momentum()).mass2();
    double mplus = (pip[0].momentum() + pi0[0].momentum()).mass2();
    double mneut = (pip[0].momentum() + pim[0].momentum()).mass2();
    unsigned int iloc = psi.decaying()[ix].pid() / 100000;
    _h_pipi[iloc]->fill(sqrt(mneut));
    _h_pipi[iloc]->fill(sqrt(mplus));
    _h_pipi[iloc]->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(_h_pipi[ix]);
    normalize(_dalitz[ix]);
  }
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(BESIII_2012_I1088606);

} ```