From CREX to CEvNS: The Weak Radius of 40Ar

Despite significant theoretical efforts, the CREX-PREX dilemma remains unresolved, preventing the reliable prediction of neutron (or weak-charge) radii that, besides their intrinsic nuclear-structure interest, often serve to quantify the impact of nuclear uncertainties in searches for new physics. Coherent elastic neutrino-nucleus scattering is a clean and attractive portal to new physics whose sensitivity may be impacted by such nuclear uncertainties. In this paper we use CREX as our main anchor, together with a strong calcium-argon correlation, to provide a robust baseline for the weak radius of ${}^{40}$Ar: $R_{\rm wk}^{\,40} = 3.452 \pm 0.028~\text{(stat)} \pm 0.022~\text{(syst)}\,\text{fm}$.The weak radius of argon is an observable highly relevant to ongoing and future liquid-argon campaigns that encodes the loss of coherence at small momentum transfers.