Rivet analyses

Mass and angluar distributions in J/ψ → γηη^′

Experiment: BESIII (BEPC)

Inspire ID: 2135117

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 106 (2022) 7, 072012

Beams: * *

Beam energies: ANY

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

Measurement of mass and angluar distributions in J/ψ → γηη^′ by BESIII. The background subtracted data were read from the plots in the paper.

Source code:`BESIII_2022_I2135117.cc`

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

namespace Rivet {


  /// @brief J/psi -> gamma eta eta'
  class BESIII_2022_I2135117 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2135117);


    /// @name Analysis methods
    /// @{

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 443);
      declare(ufs, "UFS");
      DecayedParticles PSI(ufs);
      PSI.addStable(PID::ETA);
      PSI.addStable(PID::ETAPRIME);
      declare(PSI, "PSI");
      // histos
      for (unsigned int ix = 0; ix < 3; ++ix) {
        book(_h_angle[ix], 2, 1, 1 + ix);
        book(_h_mass[ix], 1, 1, 1 + ix);
      }
      book(_h_angle[3], 1, 1, 4);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // find the J/psi decays
      static const map<PdgId, unsigned int>& mode = {{22, 1}, {221, 1}, {331, 1}};
      DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
      for (unsigned int ix = 0; ix < PSI.decaying().size(); ++ix) {
        if (!PSI.modeMatches(ix, 3, mode)) continue;
        const Particle& eta = PSI.decayProducts()[ix].at(221)[0];
        const Particle& etap = PSI.decayProducts()[ix].at(331)[0];
        const Particle& gam = PSI.decayProducts()[ix].at(22)[0];
        double mEE = (eta.momentum() + etap.momentum()).mass();
        double mEG = (gam.momentum() + eta.momentum()).mass();
        if (abs(mEG - 1.019461) < 0.04) continue;
        _h_mass[0]->fill(mEE);
        _h_mass[1]->fill(mEG);
        _h_mass[2]->fill((gam.momentum() + etap.momentum()).mass());
        // angles
        LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
            PSI.decaying()[0].momentum().betaVec());
        FourMomentum pGamma = boost1.transform(gam.momentum());
        FourMomentum pEE = boost1.transform(eta.momentum() + etap.momentum());
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pEE.betaVec());
        Vector3 axis2 = boost2.transform(boost1.transform(eta.momentum())).p3().unit();
        double cTheta = pGamma.p3().unit().dot(axis2);
        _h_angle[3]->fill(cTheta);
        if (mEE > 1.5 && mEE < 1.7)
          _h_angle[0]->fill(cTheta);
        else if (mEE > 1.7 && mEE < 2.)
          _h_angle[1]->fill(cTheta);
        else if (mEE > 2. && mEE < 3.2)
          _h_angle[2]->fill(cTheta);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 4; ++ix) {
        normalize(_h_angle[ix], 1., false);
        if (ix < 3) normalize(_h_mass[ix], 1., false);
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_mass[3], _h_angle[4];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2022_I2135117);

}

Rivet analyses

Mass and angluar distributions in J/ψ → γηη′

Source code:BESIII_2022_I2135117.cc

Mass and angluar distributions in J/ψ → γηη^′

Source code:`BESIII_2022_I2135117.cc`