Weak-charge radius of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mi>Ar</mml:mi> <mml:mprescripts/> <mml:none/> <mml:mn>40</mml:mn> </mml:mmultiscripts> </mml:math> : From CREX constraints to <mml:math xmlns:mml

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 I use CREX as the basis, together with a strong calcium-argon correlation, to provide a robust baseline for the weak radius of $^{40}\mathrm{Ar}$: ${R}_{\mathrm{wk}}^{40}=3.452\ifmmode\pm\else\textpm\fi{}0.028\phantom{\rule{4pt}{0ex}}\text{(stat)}\ifmmode\pm\else\textpm\fi{}0.022\phantom{\rule{4pt}{0ex}}\text{(syst)}\phantom{\rule{0.16em}{0ex}}\text{fm}$. 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.