LAUSR

We investigate whether transition radiation from a particle shower crossing the interface between Earth and air and induced by an Earth-skimming neutrino can explain the upward event announced recently by the ANITA Collaboration. While the properties of the observed signal can in principle be explained with transition radiation, the flux necessary for a successful explanation is in tension with the current best limits from the Pierre Auger Observatory, the IceCube neutrino detector and the ANITA balloon. We also show that in this scenario, the direction of the incoming neutrino is determined precisely to within a few degrees, from the polarization properties of the observed events and thanks to the Earth opacity to ultra high energy neutrinos.