Search for Extremely-High-Energy Neutrinos and First Constraints on the Ultrahigh-Energy Cosmic-Ray Proton Fraction with IceCube. - Abbasi R; Ackermann M; Adams J; Agarwalla SK; Aguilar JA; Ahlers M; Alameddine JM; Amin NM; Andeen K; Argüelles C; Ashida Y; Athanasiadou S; et al. (Physical review letters, 2025)