Limit on Ultra High Energy neutrino flux.

摘要

We present results from the first search for Ultra High Energy (UHE) neutrinos performed on data collected in 2003 with Transient Waveform Recorders (TWR) of the AMANDA experiment. A search for a diffusely distributed flux of UHE neutrinos shows no events, leading to a flux limit, summed over all flavors E2Falln ≤ 1.69 x 10-2 GeV cm-2 s-1 sr-1 (90% C.L.) for 10 15 eV Enu 1018.7 eV. The limit is the most stringent placed to date. A number of model predictions different from the E-2 spectrum have been tested and some have been rejected at a 90% C.L. Limits on diffuse nu-fluxes for other assumed spectral indices are included. We also report results from the atmospheric neutrino analysis performed on the same data set. A search of the northern hemisphere for localized event clusters shows no statistically significant excess, thus a flux limit is calculated. We show that UHE results can limit the flux from point sources in the southern sky. The flux limit at 90% C.L. as a function of declination, delta, is E2Fpoint n (sin delta) ≤ [2.8 x e-(2 sin delta)] x 10-6 GeV cm-2 s-1 with a 12% fit uncertainty, valid for -0.98 sin(delta) 0, and for the energy range 1015 eV E 1018.7 eV. Finally, we discuss a model-dependent constraint on the extragalactic point flux that is determined from the diffuse flux limit. We show that the maximum flux from extragalactic point sources is E2(dN nu/dE) ≤ 2.3 x 10-9 ( Lnu/1045erg/s)1/3 GeV cm-2 s-1 if the ensemble of sources is characterized by an average neutrino luminosity of Lnu = 1045 erg/s. The constraint depends only slightly on factors such as the luminosity distribution, the assumed spectral index, time variability and beaming of the source. The model-dependent constraint on the point flux is a factor twenty lower than present experimental limits from direct searches.