Rivet analyses

J/ψ → e⁺e⁻η decays

Experiment: BESIII ()

Inspire ID: 1697377

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D99 (2019) no.1, 012006

Beams: * *

Beam energies: ANY

Run details: - Events with J/psi decays, either particle guns or collisions.

Differential decay rates for J/ψ → e⁺e⁻η decays.

Source code:`BESIII_2018_I1697377.cc`

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

namespace Rivet {


  /// @brief $J/\psi\to e^+e^-\eta$ decays
  class BESIII_2018_I1697377 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1697377);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(UnstableParticles(), "UFS");
      // Book histograms
      book(_h_m, 1, 1, 1);
    }


    void findDecayProducts(const Particle & mother, unsigned int & nstable, unsigned int & neta,
                           unsigned int & nep, unsigned int & nem, FourMomentum & ptot) {
      for(const Particle & p : mother.children()) {
        int id = p.pid();
        if (id == PID::EMINUS ) {
          ++nem;
          ++nstable;
          ptot += p.momentum();
        }
        else if (id == PID::EPLUS) {
          ++nep;
          ++nstable;
          ptot += p.momentum();
        }
        else if (id == PID::ETA) {
          ++neta;
          ++nstable;
        }
        else if ( !p.children().empty() ) {
          findDecayProducts(p, nstable, neta,nep,nem,ptot);
        }
        else
          ++nstable;
      }
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {

      // Loop over J/psi mesons
      for (const Particle& p :  apply<UnstableParticles>(event, "UFS").particles(Cuts::pid==443)) {
        unsigned nstable(0),neta(0),nep(0),nem(0);
        FourMomentum ptot;
        findDecayProducts(p,nstable,neta,nep,nem,ptot);
        if(nstable==3 && nem==1 && nem==1 && neta==1) {
          _h_m->fill(ptot.mass());
        }
      }

    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h_m); // normalize to unity
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_m;
    /// @}

  };


  RIVET_DECLARE_PLUGIN(BESIII_2018_I1697377);

}

Rivet analyses

J/ψ → e+e−η decays

Source code:BESIII_2018_I1697377.cc

J/ψ → e⁺e⁻η decays

Source code:`BESIII_2018_I1697377.cc`