Revisiting $η'(958)$ nuclear states

TL;DR

This study addresses whether the η'(958) meson can form quasibound states in nuclei by deriving a near-threshold η'-nucleus optical potential from free-proton data in $pp\to pp\eta'$ and $\gamma p\to \eta' p$. The resulting potential, incorporating Pauli correlations, is found to be weakly attractive but strongly absorptive, leading to broad widths ($\Gamma_{\eta'}$) and no clear bound-state signals in light to medium nuclei. The analysis emphasizes subthreshold dynamics near the $N^{\ast}(1895)$ resonance as a possible route to binding, albeit constrained by the need for a sizable real part of the η'N scattering length and challenging hadron-baryon models. Overall, the work clarifies why η' quasibound states have remained elusive and guides future investigations into subthreshold amplitudes and dynamical resonance effects.

Abstract

Observing $η'$-nuclear quasibound states requires that the $η'$-nuclear potential is both sufficiently attractive and weakly absorptive, as confirmed by the CBELSA/TAPS collaboration analysis of inclusive $η'$ production experiments on nuclear targets, including liquid hydrogen (LH$_2$). Here we present an alternative derivation of the $η'$-nuclear potential, constrained by near-threshold $pp\to ppη'$ and $γp\toη' p$ production experiments on a free proton. The resulting $η'$-nuclear potential is weakly attractive and strongly absorptive, to the extent that observation of clear signals of $η'$-nuclear quasibound states is unlikely. Possible exceptions resulting from the dynamics of the nearby $I=\frac{1}{2}$ $J=({\frac{1}{2}})^-$ nucleon resonance $N^{\ast}$(1895) are briefly discussed.