Amplitudes separation and strong-electromagnetic relative phase in the ψ (2S) decays into baryons

In the framework of a phenomenological model based on an effective Lagrangian, that allows us to exploit all available data, we have obtained the strong, electromagnetic and mixed strong-electromagnetic amplitudes of the ψ(2S) decays into baryon-antibaryon pairs. The analysis, repeating the procedure successfully implemented in the case of the leading vector charmonium J/ψ, revealed a new and quite intriguing phenomenon, that by itself triggered a further quite interesting finding. The phenomenon is the high affinity of the ψ(2S) meson with the ΛΛ¯ pair, at a level that cannot be justified by the model. As a consequence, we excluded the ΛΛ¯ channel from the set of experimental constraints by largely improving the description power of the model, which then led to another interesting result: the QCD regime turned out to be perturbative already at the ψ(2S) mass. Finally, the comparison with the results obtained for the J/ψ has shown that the main difference with respect to the ψ(2S) concerns the SU(3) breaking source due to the quark mass difference. As expected, consequently to its larger mass, the effects of such a difference are less important for the ψ(2S) with respect to the J/ψ meson.