Discriminating baryonium and final-state-interaction interpretations of $X(2356)$

Abstract

We revisit the $X(2356)$ enhancement observed by BESIII in $e^+e^-\toΛ\barΛη$ from the viewpoint of near-threshold dynamics. Motivated by the possibility of light $Λ\barΛ$ baryonium, we compare this interpretation with final-state-interaction (FSI) explanations within a minimal FSI-dressed pole framework. Fits of the pure-FSI, baryonium-like-pole, and mixed pole--continuum scenarios to the digitized BESIII spectrum identify the energy-dependent FSI description as providing the best balance between fit quality and model complexity. The extracted pole positions depend strongly on the amplitude parametrization, demonstrating the sensitivity of the baryonium interpretation to the treatment of the continuum. We discuss how decay channels, spin observables, and partner searches can provide complementary constraints on the dynamics underlying the enhancement.