2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/177557The hyperfine splitting for the 2S charmonium state is calculated and the predicted number is $Δ_{\rm HF}(2S) = 57 \pm 8$ MeV, being by derivation the lower bound of this splitting. It results in $M(η_c(2S))= 3630 \pm 8$ MeV, which is smaller by two standard deviations than found in the Belle experiment \cite{ref.01}, but close to the $η_c(2S)$ mass observed by the same group in the experiment $e^+e^- \to J/ψη_c$ \cite{ref.06} where $M(η_c(2S)) = 3622 \pm 12$ MeV was found.8 pages RevTexHigh Energy Physics - PhenomenologyHigh Energy Physics - Experimenttext