An investigation of seasonal variations in the atmospheric neutrino rate with the AMANDA-II neutrino telescope

Besides representing a source of background for the searches of astrophysical objects, atmospheric neutrinos are the most direct calibration source for neutrino telescopes. The characterization of this "test beam" has been, in the past, mostly based on the reconstruction of the energy spectrum and on flux measurements. In this work we investigate the amplitude and phase of possible seasonal variations in the event rate for the sample of 3329 neutrino candidates, detected with the AMANDA-II neutrino telescope in the years 2000-2003 (cfr. the AMANDA-II point source search, this conference). A mechanism that could produce such seasonal variations is the modulation of the target density for interactions of cosmic rays in the atmosphere. Its effect on the atmospheric muon rate is known and measurements have been performed using several underground detectors including AMANDA-II. Its effect on the rate of atmospheric neutrinos at energies above a few hundred GeV has not been studied before. In this paper we report about a calculation of the seasonal variations expected using a global temperature model for the atmosphere. The results are compared to the event rate of the AMANDA-II neutrino sample.