Rivet analyses

Radiative J/ψ → γη′π+π− decay

Experiment: BESIII (BEPC)

Inspire ID: 2018236

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 129 (2022) 4, 042001

Beams: * *

Beam energies: ANY

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

Measurement of the hadronic mass distribution in the decay J/ψ → γη′π+π−. The data were read from the plots in the paper. It is also not clear that any resolution effects have been unfolded.

Source code:BESIII_2022_I2018236.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/DecayedParticles.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief J/psi -> gamma eta' pi+pi-
  class BESIII_2022_I2018236 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2018236);


    /// @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)
        for (unsigned int iy = 0; iy < 2; ++iy)
          for (unsigned int iz = 1; iz < 2; ++iz) book(_h[ix][iy][iz], 1 + ix, 1 + iy, 1 + iz);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{211, 1}, {-211, 1}, {331, 1}, {22, 1}};
      DecayedParticles psi = apply<DecayedParticles>(event, "psi");
      // loop over particles
      for (unsigned int ix = 0; ix < psi.decaying().size(); ++ix) {
        if (!psi.modeMatches(ix, 4, mode)) continue;
        const Particle& eta = psi.decayProducts()[ix].at(331)[0];
        const Particle& pip = psi.decayProducts()[ix].at(211)[0];
        const Particle& pim = psi.decayProducts()[ix].at(-211)[0];
        double m1 = (pip.momentum() + pim.momentum() + eta.momentum()).mass();
        double m2 = (pip.momentum() + pim.momentum()).mass();
        for (unsigned int ix = 0; ix < 2; ++ix) {
          _h[0][ix][1]->fill(m1);
          _h[1][ix][1]->fill(m2);
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 2; ++ix)
        for (unsigned int iy = 0; iy < 2; ++iy)
          for (unsigned int iz = 1; iz < 2; ++iz) normalize(_h[ix][iy][iz], 1., false);
    }

    /// @}


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


  RIVET_DECLARE_PLUGIN(BESIII_2022_I2018236);

}