Search for neutrino-induced cascades with the AMANDA detector

We report on a search for electromagnetic and/or hadronic showers (cascades) induced by a diffuse flux of neutrinos with energies between 5 TeV and 300 TeV from extraterrestrial sources. Cascades may be produced by matter interactions of all flavors of neutrinos, and contained cascades have better energy resolution and afford better background rejection than throughgoing ${\nu }_{\mu }$-induced muons. Data taken in 1997 with the AMANDA detector were searched for events with a high-energy cascadelike signature. The observed events are consistent with expected backgrounds from atmospheric neutrinos and catastrophic energy losses from atmospheric muons. Effective volumes for all flavors of neutrinos, which allow the calculation of limits for any neutrino flux model, are presented. The limit on cascades from a diffuse flux of ${\nu }_e+{\nu }_{\mu }+{\nu }_{\tau }+{\overline{\nu }}_e+{\overline{\nu }}_{\mu }+{\overline{\nu }}_{\tau }$ is $E^2(d\Phi /dE)<\mathrm{}9.8\mathrm{}\times {10}^{-6}{\mathrm{GeV}\mathrm{}\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{sr}}^{-1},$ assuming a neutrino flavor flux ratio of 1:1:1 at the detector. The limit on cascades from a diffuse flux of ${\nu }_e+{\overline{\nu }}_e$ is $E^2(d\Phi /dE)<\mathrm{}6.5\mathrm{}\times {10}^{-6}{\mathrm{GeV}\mathrm{}\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{sr}}^{-1},$ independent of the assumed neutrino flavor flux ratio.