12-Years Observation of Seasonal Variation of Atmospheric Neutrino Flux with IceCube

TL;DR

This study analyzes 12 years of IceCube data to observe seasonal variations in atmospheric neutrino flux, confirming previous findings of discrepancies with theoretical models and revealing new hemispheric differences.

Contribution

Extended the analysis of atmospheric neutrino seasonal variation to 12 years and added Northern Hemisphere data, confirming and expanding previous observations of model discrepancies.

Findings

Southern Hemisphere slope parameter α=0.325±0.022

First observation of seasonal variation in Northern Hemisphere with α=0.731±0.222

Observed deviations from theoretical predictions and linear models

Abstract

High-energy atmospheric muon neutrinos are detected by the IceCube Neutrino Observatory with a high rate of almost a hundred thousand events per year. Being mainly produced in meson decays in cosmic-ray-induced air showers in the upper atmosphere, the flux of these neutrinos is expected to depend on atmospheric conditions and thus features a seasonal variation. The correlation between temperature fluctuations and variations of the neutrino rates can be described with a slope parameter $\alpha$, whose previous measurement with 6 years of IceCube data indicated a discrepancy to theoretical expectations. In this work, we present an update of the previous analysis, extending the statistics to 12-years of IceCube data, as well as adding a region in the Northern Hemisphere to the analysis. We estimate the slope parameter in the Southern Hemisphere to be $\alpha=0.325\pm0.022$, which confirms the previous observation of the tension between the theoretical predictions and experimental measurements with significance $>3\sigma$. Furthermore, the seasonal variation in the Northern Hemisphere has also been observed for the first time, with $\alpha=0.731\pm0.222$. Investigations into systematic effects reveal that the observations not only show a weaker correlation compared to the predictions, but also deviate from the expected linear relation between the atmospheric neutrino flux and the atmospheric temperature.