Ultra-high energy neutrinos: upper limits to the diffuse and point fluxes

PIEGAIA; PIERRE AUGER COLLABORATION

Beijing

Congreso; 32nd International Cosmic ray Conference; 2011

With the Surface Detector of the Pierre Auger Observatory, we can detect ultra-high energy neutrinos in the sub-EeV energy range and above. Neutrinos of all flavours can interact in the atmosphere and induce inclined showers close to the ground (down-going). The sensitivity of the Surface Detector to tau neutrinos is further enhanced through the ?Earth-skimming? mechanism (up-going). Both types of neutrino interactions can be identified through the broad time structure of the signals induced in the Surface Detector stations. Two independent sets of identification criteria were designed to search for down and up-going neutrinos in the data collected from 1 January 2004 to 31 May 2010, with no candidates found. Assuming a differential flux f(E) = kE^−2, we place a 90% CL upper limit on the single flavour neutrino flux of k < 2.8 × 10^−8 GeV cm−2 s−1 sr −1 ibased on Earth-skimming neutrinos. We also show that the Auger Observatory is sensitive to ultra-high energy neutrinos from a large fraction of the sky, and we place limits on the neutrino flux from point-like sources as a function of declination, and in particular from the active galaxy Centaurus A.