S. W. Barwick

A first search for cosmogenic neutrinos with the ARIANNA Hexagonal Radio Array

The ARIANNA experiment seeks to observe the diffuse flux of neutrinos in the 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 + ν̄ 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 − 10 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.

A prototype station for ARIANNA: a detector for cosmic neutrinos

The Antarctic Ross Ice Shelf Antenna Neutrino Array (ARIANNA) is a proposed detector for ultra-high energy astrophysical neutrinos. It will detect coherent radio Cherenkov emission from the particle showers produced by neutrinos with energies above about 1017xa0eV. ARIANNA will be built on the Ross Ice Shelf just off the coast of Antarctica, where it will eventually cover about 900xa0km2 in surface area. There, the ice-water interface below the shelf reflects radio waves, giving ARIANNA sensitivity to downward-going neutrinos and improving its sensitivity to horizontally incident neutrinos. ARIANNA detector stations each will contain 4–8 antennas, which search for pulses of 50xa0MHz to 1xa0GHz radio emission from neutrino interactions. n nWe describe a prototype station for ARIANNA, which was deployed in Moore’s Bay on the Ross Ice Shelf in December 2009, discuss the design and deployment, and present some initial figures on performance. The ice shelf thickness was measured to be 572±6xa0m at the deployment site.

Time-domain response of the ARIANNA detector

Abstract The Antarctic Ross Ice Shelf Antenna Neutrino Array (ARIANNA) is a high-energy neutrino detector designed to record the Askaryan electric field signature of cosmogenic neutrino interactions in ice. To understand the inherent radio-frequency (RF) neutrino signature, the time-domain response of the ARIANNA RF receiver must be measured. ARIANNA uses Create CLP5130-2N log-periodic dipole arrays (LPDAs). The associated effective height operator converts incident electric fields to voltage waveforms at the LDPA terminals. The effective height versus time and incident angle was measured, along with the associated response of the ARIANNA RF amplifier. The results are verified by correlating to field measurements in air and ice, using oscilloscopes. Finally, theoretical models for the Askaryan electric field are combined with the detector response to predict the neutrino signature.

Radio detection of air showers with the ARIANNA experiment on the Ross Ice Shelf

Author(s): Barwick, SW; Besson, DZ; Burgman, A; Chiem, E; Hallgren, A; Hanson, JC; Klein, SR; Kleinfelder, SA; Nelles, A; Persichilli, C; Phillips, S; Prakash, T; Reed, C; Shively, SR; Tatar, J; Unger, E; Walker, J; Yodh, G | Abstract:

Design and Performance of the ARIANNA HRA-3 Neutrino Detector Systems

We report on the development, installation, and operation of the first three of seven stations deployed at the ARIANNA sites pilot Hexagonal Radio Array (HRA) in Antarctica. The primary goal of the ARIANNA project is to observe ultrahigh energy ( > 100 PeV) cosmogenic neutrino signatures using a large array of autonomous stations, each 1 km apart on the surface of the Ross Ice Shelf. Sensing radio emissions of 100 MHz to 1 GHz, each station in the array contains RF antennas, amplifiers, 1.92 G-sample/s, 850 MHz bandwidth signal acquisition circuitry, pattern-matching trigger capabilities, an embedded CPU, 32 GB of solid-state data storage, and long-distance wireless and satellite communications. Power is provided by the sun and buffered in LiFePO 4 storage batteries, and each station consumes an average of 7 W of power. Operation on solar power has resulted in ≥58% per calendar-year live-time. The stations pattern-trigger capabilities reduce the trigger rates to a few milli-Hertz with 4-sigma voltage thresholds while retaining good stability and high efficiency for neutrino signals. The timing resolution of the station has been found to be 0.049 ns, RMS, and the angular precision of event reconstructions of signals bounced off of the sea-ice interface of the Ross Ice Shelf ranged from 0.14 to 0.17 °.

Observation of classically `forbidden' electromagnetic wave propagation and implications for neutrino detection

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 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 Fermats 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.

Optimization of ARIANNA station configuration

Recent measurements of the horizontal propagation properties of radio pulses through stratified polar firn indicate that surface detectors can observe signals from neutrino interactions throughout a much larger volume than previously considered. The evidence for horizontal propagation will be briefly summarized. Motivated by this new opportunity, the ARIANNA simulation tool to assess performance was upgraded to investigate traditional antenna receivers such as LPDA and fat dipoles in any orientation, pointing direction and geometrical position. The antenna response was computed for expected depth beneath the firn-air boundary and the separation between stations was also re-optimized to maximize sensitivity at 10^18 eV. In addition, the investigations consider locations at the ARIANNA site at Moores Bay on the Ross Ice Shelf and at the South Pole. We conclude with a discussion of the ramifications of these studies.

A swimming pool array for ultra high energy showers

Abstract A very preliminary design concept for an array using water Cherenkov counters, built out of commercially available backyard swimming pools, to sample the electromagnetic and muonic components of ultra high energy showers at large lateral distances is presented. The expected performance of the pools is estimated using the observed lateral distributions by scintillator and water Cherenkov arrays at energies above 10 19 eV and simulations.