We present new limits on ultra-high energy neutrino fluxes above 10 17 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 on-line and off-line), 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 one 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 2 ν dφ/dE ν < 10 −6 GeV/(cm 2 s sr) in the energy range 10 17 < E ν < 10 20 eV. The new RICE results rule out the most intense flux model projections at 95% confidence level.

We recently derived explicit solutions of the leading-order Dokshitzer-Gribov-Lipatov-AltarelliParisi (DGLAP) equations for the Q 2 evolution of the singlet structure function Fs(x, Q 2 ) and the gluon distribution G(x, Q 2 ) using very efficient Laplace transform techniques. We apply our results here to a study of the HERA data on deep inelastic ep scattering as recently combined by the H1 and ZEUS groups. We use initial distributions F γp 2 (x, Q 2 0 ) and G(x, Q 2 0 ) determined for x < 0.1 by a global fit to the HERA data, and extended to x = 1 using the shapes of those distributions determined in the CTEQ6L and MSTW2008LO analyses from fits to other data. Our final results are insensitive at small x to the details of the extension. We obtain the singlet quark distribution Fs(x, Q 2 0 ) from F γp 2 (x, Q 2 0 ) using small non-singlet quark distributions taken from either the CTEQ6L or the MSTW2008LO analyses, evolve Fs and G to arbitrary Q 2 , and then convert the results to individual quark distributions. Finally, we show directly from a study of systematic trends in a comparison of the evolved F γp 2 (x, Q 2 ) with the HERA data, that the assumption of leading-order DGLAP evolution is inconsistent with those data.

Interactions of ultrahigh energy neutrinos of cosmological origin in large volumes of dense, radio-transparent media can be detected via coherent Cherenkov emission from accompanying electromagnetic showers. Antarctic ice meets the requirements for an e cient detection medium for a radio frequency neutrino telescope. We carefully estimate the sensitivity of realistic antennas embedded deep in the ice to 100 MHz -1 GHz signals generated by predicted neutrino uxes from active galactic nuclei. Our main conclusion is that a single radio receiver can probe a 1 km 3 volume for events with primary energy near 2 PeV and that the total number of events registered would be roughly 200 to 400 year 1 in our most conservative estimate. An array of such receivers would increase sensitivity dramatically. A radio neutrino telescope could directly observe and test our understanding of the most powerful particle accelerators in the universe, simultaneously testing the standard theory of particle physics at unprecedented energies.

The RICE experiment (Radio Ice Cherenkov Experiment) at the South Pole, co-deployed with the AMANDA experiment, seeks to detect ultra-high energy (UHE) electron neutrinos interacting in cold polar ice. Such interactions produce electromagnetic showers, which emit radio-frequency Cherenkov radiation. We describe the experimental apparatus and the procedures used to measure the neutrino flux.

We update our estimates of charged and neutral current neutrino total cross sections on isoscalar nucleons at ultrahigh energies using a global (x, Q 2 ) fit, motivated by the Froissart bound [1], to the F2 (electron-proton) structure function utilizing the most recent analysis [2] of the complete ZEUS and H1 data sets from HERA I. Using the large Q 2 , small Bjorken-x limits of the "wee" parton model, we connect the ultrahigh energy neutrino cross sections directly to the large Q 2 , small x extrapolation of our new fit, which we assume saturates the Froissart bound [1]. We compare both to our previous work [3], which utilized only the smaller ZEUS [4] data set, as well as to recent results [5] of a calculation using the ZEUS-S based global perturbative QCD parton distributions using the combined HERA I results as input. Our new results substantiate our previous conclusions [3], again predicting significantly smaller cross sections than those predicted by extrapolating pQCD calculations to neutrino energies above 10 9 GeV.

Cosmic ray events above 10 20 eV are on the verge of confronting fundamental particle physics. The neutrino is the only candidate primary among established particles capable of crossing 100 Mpc intergalactic distances unimpeded. The magnitude of νN cross sections indicated by events, plus consistency with the Standard Model at low-energy, point to new physics of massive spin-2 exchange. In models based on extra dimensions, we find that the νN cross section rises to typical hadronic values of between 1 and 100 mb at energies above 10 20 eV. Our calculations take into account constraints of unitarity. We conclude that air-showers observed with energies above 10 19 eV are consistent with neutrino primaries and extra-dimension models. An upper bound of 1-10 TeV on the mass scale at which graviton exchange becomes strong in current Kaluza-Klein models follows.

Radio Cherenkov radiation is arguably the most efficient mechanism for detecting showers from ultra-high energy particles of 1 PeV and above. Showers occuring in Antarctic ice should be detectable at distances up to 1 km. We report on electromagnetic shower development in ice using a GEANT Monte Carlo simulation. We have studied energy deposition by shower particles and determined shower parameters for several different media, finding agreement with published results where available. We also report on radio pulse emission from the charged particles in the shower, focusing on coherent emission at the Cherenkov angle. Previous work has focused on frequencies in the 100 MHz to 1 GHz range. Surprisingly, we find that the coherence regime extends up to tens of Ghz. This may have substantial impact on future radio-based neutrino detection experiments as well as any test beam experiment which seeks to measure coherent Cherenkov radiation from an electromagnetic shower. Our study is particularly important for the RICE experiment at the South Pole.

Using repeated Laplace transform techniques, along with newly-developed accurate numerical inverse Laplace transform algorithms [1,2], we transform the coupled, integral-differential NLO singlet DGLAP equations first into coupled differential equations, then into coupled algebraic equations, which we can solve iteratively. After Laplace inverting the algebraic solution analytically, we numerically invert the solutions of the decoupled differential equations. Finally, we arrive at the decoupled NLO evolved solutionswhere Fs and G are known functions-determined using the DGLAP splitting functions up to NLO in the strong coupling constant αs(Q 2 ). The functions Fs0(x) ≡ Fs(x, Q 2 0 ) and G0(x) ≡ G(x, Q 2 0 ) are the starting functions for the evolution at Q 2 = Q 2 0 . This approach furnishes us with a new tool for readily obtaining, independently, the effects of the starting functions on either the evolved gluon or singlet structure functions, as a function of both Q 2 and Q 2 0 . It is not necessary to evolve coupled integral-differential equations numerically on a two-dimensional grid, as is currently done. The same approach can be used for NLO non-singlet distributions where it is simpler, only requiring one Laplace transform. We make successful NLO numerical comparisons to two non-singlet distributions, using NLO quark distributions published by the MSTW collaboration [3], over a large range of x and Q 2 . Our method is readily generalized to higher orders in the strong coupling constant αs(Q 2 ).