Limits on the flux of diffuse ultra high energy neutrinos

PIEGAIA; PIERRE AUGER COLLABORATION

Lodz

Congreso; 31st International Cosmic ray Conference; 2009

The array of water-Cherenkov detectors of the Pierre Auger Observatory is sensitive to neutrinos of > 1 EeV of all flavours. These interact through charged and neutral currents in the atmosphere (down-going) and, for tau neutrinos, through the ?Earth skimming? mechanism (up-going). Both types of neutrinos can be identified by the presence of a broad time structure of signals in the waterCherenkov detectors in the inclined showers that they induce when interacting close to ground. Using data collected from 1 January 2004 to 28 February 2009, we present for the first time an analysis based on down-going neutrinos and place a competitive limit on the all-flavour diffuse neutrino flux. We also update the previous limit for up-going tau neutrinos. Sources of possible backgrounds and systematic uncertainties are discussed.