Paper detail

Highest Energy Neutrino Showers in EUSO

EUSO experiment, while monitoring the downward Earth atmosphere layers, may observe among common Ultra High Energy Cosmic Rays, UHECR, also High Energy Neutrino-Induced Showers either blazing upward to the detectors at high (PeVs) energies or at much higher GZK E >= 10^19 eV energies, showering horizontally in air or vertically downward. A small fraction of these upward, horizontal and vertical Shower maybe originated by direct astrophysical UHE neutrino interacting on terrestrial air layers itself; however the dominant UHE neutrino signal are Upward and Horizontal Tau Air-Showers, UPTAUS and HORTAUs (or Earth skimming neutrinos), born within widest Earth Crust Crown (Sea or Rock) Areas, by UHE nu_tau + Nuclei--> tau interactions, respectively at PeVs and GZK energies: their rate and signatures are shown in a neutrino fluence map for EUSO thresholds versus other UHE air interacting neutrino signals and backgrounds. The effective target Masses originating HORTAUs seen by EUSO may exceed (on sea) at 10^19 eV energy a wide and huge ring volume above 1/2*A_Euso*l_tau*(L_nu/2R_Earth)^2= 5130 km^3. The consequent HORTAUS event rate (even at 10% EUSO duty cycle lifetime) may deeply test the expected Z-Burst models by at least a hundred of yearly events. Even rarest but inescapable GZK neutrinos (secondary of photopion production of observed cosmic UHECR) might be discovered in a few (or a tens) horizontal shower events; in this view an extension of EUSO detectability up to E > 10^19 eV threshold is to be preferred. A wider collecting EUSO telescope (3m diameter) might be considered.