2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/41051Recently the possibility was widely discussed that a large fraction of the highest energy cosmic rays may be decay products of Z bosons which were produced in the resonant annihilation of ultrahigh energy cosmic neutrinos on cosmological relic neutrinos. If one takes this so-called Z-burst scenario seriously, one may infer the mass of the heaviest relic neutrino as well as the necessary ultrahigh energy cosmic neutrino flux from a comparison of the predicted Z-burst spectrum with the observed cosmic ray spectrum.8 pages, 11 figures, needs icrc.cls (included). Invited so-called "Highlight Talk", to appear in the Proceedings of the 27th International Cosmic Ray Conference (ICRC 2001), Hamburg, Germany, August 2001High Energy Physics - PhenomenologyAstrophysicsHigh Energy Physics - Experimenttext