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

Abstract

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 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.

arXiv comment33 pages, 14 figures, accepted for publication in JCAP

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• Ross Ice Shelf in situ radio-frequency ice attenuation
• Time Domain Response of the ARIANNA Detector
• An in situ measurement of the radio-frequency attenuation in ice at Summit Station, Greenland
• Design and Performance of the ARIANNA Hexagonal Radio Array Systems
• Radar Absorption, Basal Reflection, Thickness, and Polarization Measurements from the Ross Ice Shelf
• Measurement of the real dielectric permittivity epsilon_r of glacial ice

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• NuRadioMC: Simulating the radio emission of neutrinos from interaction to detector
• A search for cosmogenic neutrinos with the ARIANNA test bed using 4.5 years of data
• Reconstructing the neutrino energy for in-ice radio detectors
• Neutrino vertex reconstruction with in-ice radio detectors using surface reflections and implications for the neutrino energy resolution
• Probing the angular and polarization reconstruction of the ARIANNA detector at the South Pole
• Reconstructing the arrival direction of neutrinos in deep in-ice radio detectors
• Modeling in-ice radio propagation with parabolic equation methods
• In situ, broadband measurement of the radio frequency attenuation length at Summit Station, Greenland
• Long-baseline horizontal radio-frequency transmission through polar ice
• Reconstructing non-repeating radio pulses with Information Field Theory
• Impact of biaxial birefringence in polar ice at radio frequencies on signal polarizations in ultra-high energy neutrino detection
• First-principle calculation of birefringence effects for in-ice radio detection of neutrinos
• Experimental tests of sub-surface reflectors as an explanation for the ANITA anomalous events
• Broadband RF Phased Array Design with MEEP: Comparisons to Array Theory in Two and Three Dimensions
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• 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
• Measurement of the real dielectric permittivity epsilon_r of glacial ice
• Complex Analysis of Askaryan Radiation: A Fully Analytic Model in the Time-Domain
• Angular Dependence of Vertically Propagating Radio-Frequency Signals in South Polar Ice
• Complex Analysis of Askaryan Radiation: UHE-$\nu$ Identification and Reconstruction using the Hilbert Envelope of Observed Signals
• Event Reconstruction for Radio-Based In-Ice Neutrino Detectors with Neural Posterior Estimation