Simulation study for an in-situ calibration system for the measurement of the snow accumulation and the index-of-refraction profile for radio neutrino detectors

Abstract

Sensitivity to ultra-high-energy neutrinos (E > 17 eV) can be obtained cost-efficiently by exploiting the Askaryan effect in ice, where a particle cascade induced by the neutrino interaction produces coherent radio emission that can be picked up by antennas. As the near-surface ice properties change rapidly within the upper 𝒪(100 m), a good understanding of the ice properties is required to reconstruct the neutrino properties. In particular, continuous monitoring of the snow accumulation (which changes the depth of the antennas) and the index-of-refraction n(z) profile are crucial for an accurate determination of the neutrino's direction and energy. We present an in-situ calibration system that extends the radio detector station with two radio emitters to continuously monitor the firn properties within the upper 40 m by measuring the time differences between direct and reflected (off the surface) signals (D'n'R). We determine the optimal positions of two transmitters at all three sites of current and future in-ice radio detectors: Greenland, Moore's Bay, and the South Pole. For the South Pole we find that the snow accumulation Δh can be measured with a resolution of 3 mm and the parameters of an exponential n(z) profile α and z 0 with 0.04% and 0.14% precision respectively, which constitutes an improvement of more than a factor of 10 as compared to the inference of the n(z) profile from density measurements. Additionally, as this technique is based on the measurement of the signal propagation times we are not bound to the conversion of density to index-of-refraction. We quantify the impact of these ice uncertainties on the reconstruction of the neutrino vertex, direction, and energy and find that the calibration device measures the ice properties to sufficient precision to have negligible influence.

Results from the ARIANNA high-energy neutrino detector

“…This was demonstrated on the Ross Ice Shelf and provided a precision of O(1 mm) in surface elevation, which is much better than that needed to apply the D'n'R technique to neutrinos [4]. We further developed this system into an in-situ calibration system also for the index-of-refraction profile by adding a second calibration emitter and determined the optimal positions in a simulation study [14].…”

Developing new analysis tools for near surface radio-based neutrino detectors

“…The ARIANNA pilot experiment was designed to search for UHE neutrinos with seven autonomous stations configured with just 4 downward facing log-periodic dipole antennas (LP-DAs); however, several additional detector stations were constructed with 4 upward facing LPDAs to measure the flux of cosmic rays and further study detector capabilities, background rejection, and calibration techniques [25,26]. ARIANNA operated for about half a decade to explore and improve detector and analysis techniques.…”