arXiv subjects
Publications and source records attributed to Gary C. Hill.
The field of high-energy neutrino astronomy has seen rapid progress over the last 15 years, with the development and operation of the first large-volume detectors. Here, we review the motivation for construction of these large instruments and discuss what construction and physics progress has been made.
Since the early 1990s, the South Pole has been the site of the construction of the world's first under-ice Cherenkov neutrino telescopes - AMANDA and IceCube. The AMANDA detector was completed in 2000, and its successor IceCube, a kilometre scale neutrino detector, began construction in 2005. Completion of IceCube is scheduled for 2011. This paper will give an overview of the history, construction, latest physics results and potential of these detectors.
The incorporation of systematic uncertainties into confidence interval calculations has been addressed recently in a paper by Conrad et al. (Physical Review D 67 (2003) 012002). In their work, systematic uncertainities in detector efficiencies and background flux predictions were incorporated following the hybrid frequentist-Bayesian prescription of Cousins and Highland, but using the likelihood ratio ordering of Feldman and Cousins in order to produce "unified" confidence intervals. In general, the resulting intervals behaved as one would intuitively expect, i.e. increased with increasing uncertainties. However, it was noted that for numbers of observed events less than or of order of the expected background, the intervals could sometimes behave in a completely counter-intuitive fashion -- being seen to initially decrease in the face of increasing uncertainties, but only for the case of increasing signal efficiency uncertainty. In this comment, we show that the problematic behaviour is due to integration over the signal efficiency uncertainty while maximising the best fit alternative hypothesis likelihood. If the alternative hypothesis likelihood is determined by unconditionally maximising with respect to both the unknown signal and signal efficiency uncertainty, the limits display the correct intuitive behaviour.
We present a method for optimising experimental cuts in order to place the strongest constraints (upper limits) on theoretical signal models. The method relies only on signal and background expectations derived from Monte-Carlo simulations, so no bias is introduced by looking at actual data, for instance by setting a limit based on expected signal above the ``last remaining data event.'' After discussing the concept of the ``average upper limit,'' based on the expectation from an ensemble of repeated experiments with no true signal, we show how the best model rejection potential is achieved by optimising the cuts to minimise the ratio of this ``average upper limit'' to the expected signal from the model. As an example, we use this technique to determine the limit sensitivity of kilometre scale neutrino detectors to extra-terrestrial neutrino fluxes from a variety of models, e.g. active galaxies and gamma-ray bursts. We suggest that these model rejection potential optimised limits be used as a standard method of comparing the sensitivity of proposed neutrino detectors.
The AMANDA (Antarctic Muon And Neutrino Detector Array) detector, located at the South Pole station, Antarctica, was recently expanded with the addition of six new strings, completing the phase referred to as AMANDA-II. This detector has been calibrated and in operation since January 2000. The first data analyses are currently underway. In this report we present an update on the results from the AMANDA-B10 detector, which operated during the austral winter 1997.
Several large volume, high energy neutrino detectors are in operation or in the design stage. Upward going signal neutrino events must be separated from large backgrounds of downgoing cosmic ray induced atmospheric muons. To this end, a Bayesian extension of the traditional maximum likelihood reconstruction method will be described. Further, it will be shown how signals can be separated from backgrounds through integration of Bayesian posterior probability densities.
New information on the structure of the nucleon from the HERA ep collider leads to higher neutrino cross sections for the processes nu_mu + N --> mu + X needed to calculate the expected rates of astrophysical neutrino induced muons in large detectors either under construction, or in the design stage. These higher cross sections lead to higher muon rates for arrival angles where neutrino attenuation in the earth is less important. On the other hand, new estimates of AGN neutrino fluxes suggest that the expected muon rates in these detectors may be much lower than previously calculated. I use the new cross sections to calculate the expected muon rates and angular distributions in large detectors for a variety of AGN models and compare these rates with the atmospheric neutrino backrounds (from both conventional decay channels and the "prompt" charmed meson decay channels). If the lowest flux estimates are correct, there may be diffculties in determining the origin of a small excess of muons, due to the large uncertainty in the rate of the charmed meson neutrino production channel. However, the more optimistic AGN neutrino fluxes should be detectable in proposed detectors, such as DUMAND-II, AMANDA, NESTOR and Lake Baikal.