The Pierre Auger Observatory and ultra-high energy neutrinos: upper limits to the diffuse and point source fluxes

摘要

With the Surface Detector of the Pierre Auger Observatory, we can detect ultra-high energy neutrinos in thesub-EeV energy range and above. Neutrinos of all flavours can interact in the atmosphere and induce inclined showersclose to the ground (down-going). The sensitivity of the Surface Detector to tau neutrinos is further enhanced throughthe "Earth-skimming" mechanism (up-going). Both types of neutrino interactions can be identified through the broadtime structure of the signals induced in the Surface Detector stations. Two independent sets of identification criteria weredesigned to search for down and up-going neutrinos in the data collected from 1 January 2004 to 31 May 2010, with nocandidates found. Assuming a differential flux f(E) = kE2 , we place a 90% CL upper limit on the single flavourneutrino flux of k < 2.8 × 108GeV cm2s1sr1 in the energy interval 1.6 × 1017eV 2.0 × 1019eV based onEarth-skimming neutrinos and k < 1.7 × 107GeV cm2s1sr1 in the energy interval 1 × 1017eV 1 × 1020eVbased on down-going neutrinos. We also show that the Auger Observatory is sensitive to ultra-high energy neutrinos froma 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.