Neutrino-induced hyperon final-state interactions as constraints on the in-medium hyperon potential

Hyperon single-particle potentials U Y(rho) control propagation in nuclei and hyperon onset in dense matter, where they soften the neutron-star equation of state and reduce the maximum mass -- the ``hyperon puzzle''. We show that charged-current accelerator (anti)neutrino interactions on 40 Ar, producing and inside the nucleus, can constrain these potentials. At SBND and DUNE energies, the trapped- fraction and escaping-hyperon momenta vary monotonically with U and U, with a kaon-vetoed FSI-+ tag adding sensitivity. Inserted in a GM1 relativistic mean-field equation of state at established hypernuclear/ -atom depths, the same potentials give M max = 1.94,M and 1.4=1034, below the heaviest pulsars and above the GW170817 bound typical of GM1-class mean fields. A detector-level Fisher forecast yields delta U 0.3, MeV and delta U 3 - 4, MeV for fixed low-density exponent gamma. Since hyperons are produced below saturation, U(rho 0) and gamma are 99.8% anti-correlated; marginalising over gamma degrades the anchor to delta U 5.6, MeV (1.3, MeV with a plus or minus 0.2 prior), while delta U is unchanged. For U, comparable systematics arise from hyperon-nucleon final-state cross sections (-5/ + 2, MeV) and the exit-shift/gradient transport prescription (-6, MeV). For U, the same YN uncertainty biases the fit by O(150), MeV; removing the+ tag does not cure this, because the momentum spectrum carries most U information and is itself YN-sensitive. The low-density U anchor is a robust handle, at several-MeV rather than sub-MeV precision. A joint fit with terrestrial and heavy-ion priors gives M max = 2.21+0.04-0.15,, Msun, set mainly by the external c prior.