Neutrino identification with Auger and ντ flux limit

The surface detector array of the Pierre Auger Observatory is sensitive to Earth-skimming ντ. The topological properties of such showers are quite different from hadronic events. Neutrino-induced showers are characterized by very elongated and asymmetric footprints and a significant electromagnetic component. Electrons and gammas produce broad timing signals, whereas hadronic showers give rise to signals mostly due to the surviving secondary muons with a shorter signal in time with respect to an electromagnetic signal. The data collected between 1st January 2004 and 31st August 2007 is used to place an upper limit on the diffuse flux of ντ. Over this perio there is not a single event that fulfills the selection criteria. The limit for an E−2 differential energy spectrum at 90% C.L. is: .