Speaker
Description
A significant neutrino event with an estimated energy between 72$\,\mathrm{PeV}$ and 2.6$\,\mathrm{EeV}$ was observed by the KM3NeT experiment (KM3-230213A). When interpreted as cosmogenic in origin, this event can provide new constraints on the observed fraction of ultra-high-energy (UHE) protons beyond the ankle and the cosmological evolution of their sources. In this contribution, we present the best fit to the spectrum and composition of ultra-high-energy cosmic rays (UHECRs) that is consistent with multi-messenger constraints, including the detection of a single neutrino event by the KM3NeT detector at the energy range of KM3-230213A. Our results indicate that the detection of a single neutrino event at the energy range of KM3-230213A solely with the KM3NeT exposure requires strongly evolving UHE proton sources, which is consistent with different classes of high-luminosity active galactic nuclei. On the other hand, including the null observations from the Pierre Auger and IceCube observatories disfavors such strong evolution but allows for moderately positive, flat, and slightly negative evolutions for the sources of UHE protons. In both cases, the observed proton fraction of UHECRs is primarily constrained by the composition data to be ${\sim\,} 20\%$ at 20$\,\mathrm{EeV}$.
