Determination of Absolute Neutrino Masses from Bursts of Z Bosons in Cosmic Rays

Ultrahigh energy neutrinos [Formula presented] scatter on relic neutrinos [Formula presented] producing Z bosons, which can decay hadronically producing protons (Z burst). We compare the predicted proton spectrum with the observed ultrahigh energy cosmic ray (UHECR) spectrum and determine the mass of the heaviest [Formula presented] via a maximum likelihood analysis. Our prediction depends on the origin of the powerlike part of the UHECR spectrum: [Formula presented] for Galactic halo and [Formula presented] for extragalactic origin. The necessary [Formula presented] flux should be detected in the near future.