A low-threshold ultrahigh-energy neutrino search with the Askaryan Radio Array

Abstract

In the pursuit of the measurement of the still-elusive ultrahigh-energy (UHE) neutrino flux at energies of order EeV, detectors using the in-ice Askaryan radio technique have increasingly targeted lower trigger thresholds. This has led to improved trigger-level sensitivity to UHE neutrinos. Working with data collected by the Askaryan Radio Array (ARA), we search for neutrino candidates at the lowest threshold achieved to date, leading to improved analysis-level sensitivities. A neutrino search on a data set with 208.7~days of livetime from the reduced-threshold fifth ARA station is performed, achieving a 68\% analysis efficiency over all energies on a simulated mixed-composition neutrino flux with an expected background of $0.10_{-0.04}^{+0.06}$ events passing the analysis. We observe one event passing our analysis and proceed to set a neutrino flux limit using a Feldman-Cousins construction. We show that the improved trigger-level sensitivity can be carried through an analysis, motivating the Phased Array triggering technique for use in future radio-detection experiments. We also include a projection using all available data from this detector. Finally, we find that future analyses will benefit from studies of events near the surface to fully understand the background expected for a large-scale detector.

15 pages, 8 figures

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Cited by in corpus (9)

• Detector Requirements for Model-Independent Measurements of Ultrahigh Energy Neutrino Cross Sections
• Radio Detection of High Energy Neutrinos in Ice
• The flavor composition of ultra-high-energy cosmic neutrinos: measurement forecasts for in-ice radio-based EeV neutrino telescopes
• Observation of In-ice Askaryan Radiation from High-Energy Cosmic Rays
• 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
• In-ice Askaryan Emission from Air Showers: Implications for Radio Neutrino Detectors
• Complex Analysis of Askaryan Radiation: UHE-$\nu$ Identification and Reconstruction using the Hilbert Envelope of Observed Signals
• Particle Astrophysics with High and Ultrahigh Energy Neutrinos
• Progress Towards a Diffuse Neutrino Search in the Full Livetime of the Askaryan Radio Array