Search for a diffuse flux of high-energy extraterrestrial neutrinos with the NT200 neutrino telescope

Abstract We present the results of a search for high-energy extraterrestrial neutrinos with the Baikal underwater Cherenkov detector NT200, based on data taken in 1998–2003. Upper limits on the diffuse fluxes of ν e  +  ν μ  +  ν τ , predicted by several models of AGN-like neutrino sources, are derived. For an E −2 behavior of the neutrino spectrum, our limit is E 2 Φ ν ( E )  −7  cm −2  s −1  sr −1  GeV over an neutrino energy range 2 × 10 4 –5 × 10 7  GeV. The upper limit on the resonant ν ¯ e diffuse flux is Φ ν ¯ e 3.3 × 10 - 20 cm - 2 s - 1 sr - 1 GeV - 1 .