Disentangling isospin violation in charmonia decaying into $\Xi \overline{\Xi }$ pairs

Abstract

Based on a model-independent isospin decomposition, we perform a data-driven analysis of $J/\psi$ and $\psi (2S)$ decays into $\Xi \bar{\Xi }$ pairs by leveraging the full set of observables from high-statistics BESIII data. We find that the isospin-violating amplitudes are predominantly driven by the electric couplings, with magnitudes reaching approximately 10%, contrasting with the smaller magnetic contributions of about 3%. A partial-wave analysis further reveals that $S$-wave isospin violation is comparable to the $D$-wave contribution.