Rivet analyses

Mass distributions in J/ψ → π+π−π0

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/ψ → π+π−π0, data read from plots in paper and may not be corrected. The angluar cuts used in this analysis enhance the ρπ component and supress the higher resonances.

Source code:KEDR_2022_I2593308.cc

// -*- 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);

}