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

Abstract

We present the results of a new analysis of data taken in 1998-2002 for a search for high-energy extraterrestrial neutrinos. The analysis is based on a full reconstruction of high-energy cascade parameters: vertex coordinates, energy and arrival direction. Upper limits on the diffuse fluxes of all neutrino flavors, predicted by several models of AGN-like neutrino sources are derived. For an ${\bf E^{-2}}$ behavior of the neutrino spectrum, our limit is ${\bf E^{2} F_{\nu}(E) < 2.9 \times 10^{-7}}$ cm${\bf ^{-2}}$ s${\bf ^{-1}}$ sr${\bf ^{-1}}$ GeV over a neutrino energy range ${\bf 2 \times 10^4 \div 2 \times 10^7}$ GeV. This limit is by a factor of 2.8 more stringent than a limit obtained with a previous analysis.