•C.K. Guérard, H. Blümer, D. Heck, B. Keilhauer, S.S. Ostapchenko und T. Thouw
Forschungszentrum und Universität Karlsruhe, Institut für Kernphysik, Postfach 3640, 76021 Karlsruhe

Monte Carlo simulations of EAS have shown that for 10¹⁹ eV primaries and depths exceeding 3,000 g/cm² (equivalent to 70^° zenith angles) the electromagnetic component is very small and originates mainly from muon decay. Horizontal cosmic rays traversing Earth's atmosphere at an altitude of 18 km already encounter an equivalent column depth of ~ 6,000 g/cm². Fluorescence Detectors (FD) detect air fluorescence which is proportional to the energy deposited by charged particles. We show that nearly horizontal EAS originated by primaries with energies smaller than 100 EeV overpassing a FD will pass undetected unless they are neutrinos (or any other exotic weakly interacting particle) which happen to interact deep in the atmosphere. We compute the acceptance of the Southern Pierre Auger FD to such showers and, based on different neutrino flux and neutrino interaction models, find that, in the best scenario, the rate for detection of showers arising from (n_e+[`(n)]_e)N via charged-current interactions will be ~ 1/y.