Characterizing IceTop Response to Low-Energy Air Showers

TL;DR

IceTop scaler rates offer a proxy for modulations in Galactic and solar cosmic-ray flux. The study combines a long-term data set (2013–2024) with Monte Carlo simulations of low-energy air showers (CORSIKA with FLUKA and Sibyll, Geant4 within the IceCube framework) to map detector counts to primary CR spectra across discriminator thresholds. A pressure-correction framework using a monthly barometric coefficient $β$ and reference pressure $P_0$ standardizes rates to isolate solar- and heliospheric-driven variations while accounting for snow depth and MB temperature. The results demonstrate sensitivity to solar events and atmospheric conditions, enabling prompt detection of solar energetic particle events and Forbush decreases and informing detector calibration.

Abstract

This study evaluates the response of the IceTop tanks to low-energy air showers in the GeV to TeV energy range based on simulated and measured count rates. Correlating this response with primary cosmic rays provides a tool to study Galactic and solar cosmic-ray flux modulations, particularly for solar particle events. We present long-term behavior of the IceTop scaler rates for a range of discriminator thresholds to better understand and calibrate the detector's response to changing environmental conditions.

Figures (4)

• Figure 1: Long-term scaler count rates for IceTop DOM 16–61 from May 2013 to December 2024. Panel (a) shows uncorrected (gray) and pressure-corrected (blue) count rates using daily time bins. Panel (b) displays the corresponding atmospheric pressure in mbar. The pressure correction is applied monthly using the barometric coefficient.
• Figure 2: Long-term variations (May 2013 -- December 2024) of IceTop scaler count rates corrected to 680 mbar, mainboard (MB) temperatures, and snow depth. The top panel shows scaler count rates for the following DOMs and their corresponding discriminator thresholds: DOM 05–61, 4.7 PE (red), DOM 16–61, 8.3 PE (blue), and DOM 66–61, 23.0 PE, (black). The middle panel displays daily-averaged mainboard temperatures; the gap in data results from a transition between two data sources. The bottom panel presents in situ snow depth measurements, noting the limited sampling frequency of 2–3 points per year.
• Figure 3: Charge spectrum observed by a high-gain DOM of the IceTop tank (buried under 2.46 m snow) in response to secondary particles from 1 GeV -- 125 TeV primary protons, where each entry corresponds to a single particle deposition. In addition, the gray line indicates the spectrum of total charge in the tank - higher due to presence of multiple particles contributing to the charge.
• Figure 4: Ground-level kinetic energy spectra of muons and EM particles originating from baryon grandmother, under different seasonal atmospheric models. The left panel shows particles coming predominantly from $\pi^{0}$'s, while the right plot shows mainly products of $\pi^{\pm}$'s. See text for more details.