Investigation of backgrounds for horizontal neutrino showers at ultra-high energies

The Pierre Auger Observatory can be used to search for neutrino-induced air showers. A possible signature is a near-horizontal event developing very deeply in the atmosphere (at depths exceeding a few thousand g/cm2). We study the background to such events from: (1) high-energy muons produced in primary proton events, which may propagate deeply into the atmosphere; (2) primary photons, which may develop late due to a suppression of the Bethe-Heitler cross-section by the LPM effect. For the investigations, we use high-statistics shower libraries generated on the ALiCEnext computer cluster at the University of Wuppertal. The rates of background events are compared with various flux models of ultra-high energy neutrino production. (orig.)