Radio Signatures of Cosmic-Ray Particle Showers in Deep In-Ice Antennas

TL;DR

The paper addresses validating in-ice radio detection for ultra-high-energy neutrinos by characterizing the radio signatures of cosmic-ray showers as a background using the FAERIE framework, which combines CoREAS and GEANT4. It simulates in-air and in-ice emissions for primary energies in $E=[10^{16.5},10^{17},10^{17.5}]\,\mathrm{eV}$ and lines up zenith angles up to $50^\circ$, with deep in-ice antennas and surface components. Key findings show that the in-ice component dominates for vertical showers, while the in-air component grows with zenith angle, and that surface timing, double-pulse events, and polarization (Hpol/Vpol) patterns provide robust cosmic-ray identification—a crucial step for neutrino–cosmic-ray discrimination. These results offer practical pathways to calibrate deep in-ice detectors and validate the in-ice detection principle for experiments like ARA and RNO-G.

Abstract

To detect ultra-high-energy neutrinos, experiments such as ARA and RNO-G target the radio emission induced by these particles as they cascade in the ice, using deep in-ice antennas at the South Pole or in Greenland. In this context, it is essential to first characterize the in-ice radio signature from cosmic-ray-induced particle showers, which constitute a primary background for neutrino detection, and represent the fist in-situ detection of in-ice particle cascades with radio antennas. This characterization will help validate the detection principle and assist in calibration. To achieve this goal, we used FAERIE, the "Framework for the simulation of Air shower Emission of Radio for in-Ice Experiments", that combines CoREAS and GEANT4 to simulate the radio emission of cosmic ray showers deep in the ice. Using this tool, we analyze in-ice radio signatures of cosmic-ray showers, including polarization, timing, and radiation energy, as well as their dependence on shower parameters. These insights will facilitate the first cosmic-ray detections and improve cosmic-ray/neutrino discrimination.

Figures (5)

• Figure 1: Interpolated electric field map of ( left) the in-air emission and ( right) the in-ice emission seen at a depth of 100 meters below the ice surface, for a vertical proton-induced shower with primary energy $E=10^{16.5}\, \rm eV$.
• Figure 2: Left: Radiation energy at a depth of 100 meters, for the in-air (blue curve) and the in-ice (orange curve) emission, as a function of the zenith angle, for proton-induced showers with primary energy $E = 10^{17.5}\, \rm eV$. Right: Ratio of the in-air and in-ice radiation energies at a depth of 100 meters, as a function of the zenith angle, for proton-induced showers with three different primary energies $[10^{16.5}, 10^{17}, 10^{17.5}]\, \rm eV$. The dashed black line indicates the limit where the ratio is equal to 1.
• Figure 3: Left: All-zenith distribution of time delays between signals from surface antennas and deep antennas at a depth of 100 meters for proton-induced showers with a primary energy $E= 10^{17.5}\, \rm eV$, from FAERIE simulations. Right: Mean (dots) and standard deviation (error bars) of the time delays between surface and 100-m deep antennas for $E=10^{17.5} \, \rm eV$.
• Figure 4: ( Left) Normalized all-zenith double pulses density map at depth of 100 m for proton showers with energy $E=10^{17.5}\, \rm$ eV. ( Right) Double pulses rate for each electric field channel as a function of the shower zenith angle.
• Figure 5: Hpol over Vpol radiation energy ratio for ( left) the in-air and ( right) the in-ice emission as a function of the shower zenith angle, for different primary energies.