Rivet analyses

title: KEDR_2022_I2593308

Mass distributions in $J/\psi\to\pi^+\pi^-\pi^0$

Experiment: KEDR (VEPP-4M)

Inspire ID: 2593308

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2211.13520

Beams: * *

Beam energies: ANY

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

Measurement of mass distributions in $J/\psi\to\pi^+\pi^-\pi^0$, data read from plots in paper and may not be corrected. The angluar cuts used in this analysis enhance the $\rho\pi$ component and supress the higher resonances.

Source code:KEDR_2022_I2593308.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi -> pi+pi-pi0 class KEDR_2022_I2593308 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(KEDR_2022_I2593308);


/// @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");
  // histograms
  for (size_t ix = 0; ix < 3; ++ix) {
    book(_h_pipi[ix], 1, 1, 1 + ix);
  }
}


/// 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 (size_t 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].mom() + pi0[0].mom()).mass();
    double mplus = (pip[0].mom() + pi0[0].mom()).mass();
    double mneut = (pip[0].mom() + pim[0].mom()).mass();
    double Cminus = pim[0].mom().p3().unit().dot(pi0[0].mom().p3().unit());
    double Cplus = pip[0].mom().p3().unit().dot(pi0[0].mom().p3().unit());
    double Cneut = pip[0].mom().p3().unit().dot(pim[0].mom().p3().unit());
    if (Cminus + Cplus + Cneut > -1.075) continue;
    if (Cneut > Cminus && Cneut > Cplus) _h_pipi[0]->fill(mneut);
    if (Cplus > Cminus && Cplus > Cneut) _h_pipi[1]->fill(mplus);
    if (Cminus > Cplus && Cminus > Cneut) _h_pipi[2]->fill(mminus);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_pipi, 1.0, false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_pipi[3];
/// @}

};

RIVET_DECLARE_PLUGIN(KEDR_2022_I2593308);

} ```