The RICE experiment seeks observation of ultra-high energy (UHE; $E_{\nu }>{10}^{17}\mathrm{eV}$) neutrinos interacting in Antarctic ice, by measurement of the radio frequency (RF) Cherenkov radiation resulting from the collision of a neutrino with an ice molecule. RICE was initiated in 1999 as a first-generation prototype for an eventual, large-scale in-ice UHE neutrino detector. Herein, we present updated limits on the diffuse UHE neutrino flux, based on 12 years of data taken between 1999 and 2010. We find no convincing neutrino candidates, resulting in 95% confidence-level model-dependent limits on the flux $E_{\nu }^{2}d\varphi /d{E}_{\nu }<0.5\times {10}^{-6}\mathrm{GeV}/({\mathrm{cm}}^2\mathrm{s}\mathrm{\text{−}}\mathrm{sr})$ in the energy range ${10}^{17}<E_{\nu }<{10}^{20}\mathrm{eV}$, or approximately a twofold improvement over our previously published results. Recently, the focus of RICE science has shifted to studies of radio frequency ice properties as the RICE experimental hardware has been absorbed into a new experimental initiative (the Askaryan Radio Array, or “ARA”) at the south pole. ARA seeks to improve on the RICE sensitivity by approximately 2 orders of magnitude by 2017 and thereby establish the cosmogenic neutrino flux. As detailed herein, RICE studies of Antarctic ice demonstrate that both birefringence and internal layer RF scattering result in no significant loss of ARA neutrino sensitivity, and, for the first time, verify in situ the decrease in attenuation length with depth into the Antarctic ice sheet.

• Received 21 June 2011

DOI:https://doi.org/10.1103/PhysRevD.85.062004