The ARIANNA experiment seeks to observe the diffuse flux of neutrinos in the 10 8 − 10 10 GeV energy range using a grid of radio detectors at the surface of the Ross Ice Shelf of Antarctica. The detector measures the coherent Cherenkov radiation produced at radio frequencies, from about 100 MHz to 1 GHz, by charged particle showers generated by neutrino interactions in the ice. The ARIANNA Hexagonal Radio Array (HRA) is being constructed as a prototype for the full array. During the 2013-14 austral summer, three HRA stations collected radio data which was wirelessly transmitted off site in nearly real-time. The performance of these stations is described and a simple analysis to search for neutrino signals is presented. The analysis employs a set of three cuts that reject background triggers while preserving 90% of simulated cosmogenic neutrino triggers. No neutrino candidates are found in the data and a model-independent 90% confidence level Neyman upper limit is placed on the all flavor ν +ν flux in a sliding decade-wide energy bin. The limit reaches a minimum of 1.9×10 −23 GeV −1 cm −2 s −1 sr −1 in the 10 8.5 − 10 9.5 GeV energy bin. Simulations of the performance of the full detector are also described. The sensitivity of the full ARIANNA experiment is presented and compared with current neutrino flux models.

Ongoing experimental efforts in Antarctica seek to detect ultra-high energy neutrinos by measurement of radio-frequency (RF) Askaryan radiation generated by the collision of a neutrino with an ice molecule. An array of RF antennas, deployed either in-ice or in-air, is used to infer the properties of the neutrino. To evaluate their experimental sensitivity, such experiments 1 arXiv:1804.10430v2 [astro-ph.IM] 13 Jul 2018 require a refractive index model for ray tracing radio-wave trajectories from a putative in-ice neutrino interaction point to the receiving antennas; this gives the degree of signal absorption or ray bending from source to receiver.The gradient in the density profile over the upper 200 meters of Antarctic ice, coupled with Fermat's least-time principle, implies ray "bending" and the existence of "forbidden" zones for predominantly horizontal signal propagation at shallow depths. After re-deriving the formulas describing such shadowing, we report on experimental results that, somewhat unexpectedly, demonstrate the existence of electromagnetic wave transport modes from nominally shadowed regions. The fact that this shadow-signal propagation is observed both at South Pole and the Ross Ice Shelf in Antarctica suggests that the effect may be a generic property of polar ice, with potentially important implications for experiments seeking to detect neutrinos.

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ABSTRACT. Radio-glaciological parameters from Moore's Bay, in the Ross Ice Shelf, have been measured. The thickness of the ice shelf in Moore's Bay was measured from reflection times of radio-frequency pulses propagating vertically through the shelf and reflecting from the ocean, and is found to be 576 ± 8 m. Introducing a baseline of 543±7 m between radio transmitter and receiver allowed the computation of the basal reflection coefficient, R, separately from englacial loss. The depth-averaged attenuation length of the ice column, L is shown to depend linearly on frequency. The best fit (95% confidence level) is L(ν) = (460 ± 20) − (180 ± 40)ν m (20 dB/km), for the frequencies ν =[0.100-0.850] GHz, assuming no reflection loss. The mean electric-field reflection coefficient is √ R = 0.82 ± 0.07 (-1.7 dB reflection loss) across [0.100-0.850] GHz, and is used to correct the attenuation length. Finally, the reflected power rotated into the orthogonal antenna polarization is less than 5% below 0.400 GHz, compatible with air propagation. The results imply that Moore's Bay serves as an appropriate medium for the ARIANNA high energy neutrino detector.

A measurement of Newton's gravitational constant G has been made with a cryogenic torsion pendulum operating below 4 K in a dynamic mode in which G is determined from the change in torsional period when a field source mass is moved between two orientations. The source mass was a pair of copper rings that produced an extremely uniform gravitational field gradient, whereas the pendulum was a thin fused silica plate, a combination that minimized the measurement's sensitivity to error in pendulum placement. The measurement was made using an as-drawn CuBe torsion fibre, a heat-treated CuBe fibre, and an as-drawn Al5056 fibre. The pendulum operated with a set of different large torsional amplitudes. The three fibres yielded high Q -values: 82 000, 120 000 and 164 000, minimizing experimental bias from fibre anelasticity. G -values found with the three fibres are, respectively: {6.67435(10),6.67408(15),6.67455(13)}×10 −11  m 3  kg −1  s −2 , with corresponding uncertainties 14, 22 and 20 ppm. Relative to the CODATA2010 G -value, these are higher by 77, 37 and 107 ppm, respectively. The unweighted average of the three G -values, with the unweighted average of their uncertainties, is 6.67433(13)×10 −11  m 3  kg −1  s −2  (19 ppm).