Comments on ${\eta }^{\prime }$ nuclei and on the $\Lambda$ binding energy of the hypertriton

Abstract

I briefly discuss two apparent puzzles: (i) is the observation of ${\eta }^{\prime }$(958) bound states in ${}^{11}$C at GSI [1] compatible with a nearly vanishing real part of ${\eta }^{\prime }N$ scattering length [2]? and (ii) is the $\Lambda$ binding energy of the hypertriton (${{}_{\Lambda }}^3$H), the lightest particle-stable hypernucleus, very small (63${}_{-31}^{+38}$ keV, J-PARC E73 [3]) or very large (523$\pm$76 keV, MAMI [4])? Here, I suggest that MAMI's observed weak-decay pion momentum peak originates from ${{}_{\Lambda }}^7$He, not from ${{}_{\Lambda }}^3$H \cite{Gal26}.

arXiv commentTalk given at MESON2026, Krakow, June 2026