RICE limits on the diffuse ultrahigh energy neutrino flux

We present new limits on ultrahigh energy neutrino fluxes above 10¹⁷ eV based on data collected by the Radio Ice Cherenkov Experiment (RICE) at the South Pole from 1999--2005. We discuss estimation of backgrounds, calibration and data analysis algorithms (both online and offline), procedures used for the dedicated neutrino search, and refinements in our Monte Carlo (MC) simulation, including recent in situ measurements of the complex ice dielectric constant. An enlarged data set and a more detailed study of hadronic showers results in a sensitivity improvement of more than 1 order of magnitude compared to our previously published results. Examination of the full RICE data set yields zero acceptable neutrino candidates, resulting in 95% confidence-level model-dependent limits on the flux E_ν²dφ/dE_ν<10^-6 GeV/(cm² s sr) in the energy range 10¹⁷<E_ν<10²⁰ eV. The new RICE results rule out the most intense flux model projections at 95% confidence level.