Atmospheric seasoning
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Date
2024
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Abstract
Besides the detection of astrophysical neutrinos, atmospheric neutrinos from cosmicray-
induced air showers are detected at unprecedented statistics with the IceCube Neutrino
Observatory. The conventional component of the atmospheric neutrino flux is
produced in decays of kaons and pions. Due to seasonal changes in the atmospheric
temperature, the neutrino flux undergoes a seasonal variation. When the temperature
increases, the atmosphere expands, and more neutrinos are expected to be produced.
Additionally, the seasonal variation increases with energy, as parent particles interact
at higher altitudes in the atmosphere, where seasonal temperature variations are larger.
The interaction cross section increases with energy and the probability for the parent
meson to decay increases. The investigation of seasonal variations serves as an accurate
background determination in the search for astrophysical neutrinos and the study of
hadronic interactions in atmospheric particle cascades.
In this thesis, seasonal variations in the atmospheric neutrino flux are measured energydependently
for the first time based on 11.5 years of IceCube data. The determination
of the neutrino energy presents an ill-conditioned inverse problem, requiring to infer
the energy from measured detector quantities. This challenge is addressed by the
Dortmund Spectrum Estimation Algorithm (DSEA+), which utilizes machine learning
methods to unfold the neutrino energy. The determined variation strength is compared
to theoretical predictions from MCEq, and in particular to the calculation with the
atmospheric model NRLMSISE-00.
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Keywords
Seasonal variations, Atmospheric muon neutrinos, Unfolding, IceCube, Neutrinos, Cosmic ray air showers, Atmosphere