Charmonium decays into proton-antiproton and a quark-diquark model for the nucleon.

Abstract

A quark-diquark model of the nucleon is applied to a perturbative QCD description of several decays of the charmonium family: ${\ensuremath{\eta}}_{c}, {\ensuremath{\chi}}_{c0,c1,c2,} {f}_{c2}\ensuremath{\rightarrow}p\overline{p}$. Both experimental data and theoretical considerations are used to fix the parameters of the model. The decay rates for the $\ensuremath{\chi}'\mathrm{s}$ and for the ${\ensuremath{\eta}}_{c}$ cannot be made to simultaneously agree with the experimental results: we can obtain a good agreement with the existing data on the $\ensuremath{\chi}'\mathrm{s}$, but the values for the decay of the ${\ensuremath{\eta}}_{c}$ are then found to be much smaller than the data. The available experimental information is also discussed. Our formalism provides a general framework for the computation of the decay amplitudes of any $^{2S+1}L_{J}$, $C=+1$, heavy-quarkonium state into a hadron-antihadron pair. The explicit expression for the decay into two photons is also given.