KATRIN: A Direct Approach to the Unbearable Lightness of Neutrinos

The Karlsruhe Tritium Neutrino experiment (KATRIN) experiment is a direct search for the absolute mass scale of the neutrino, based on the kinematics of tritium β decay. Combining an intense windowless, gaseous tritium source with a precise integrating energy filter, KATRIN has been making precision scans of the endpoint region of the tritium β spectrum since 2019. Our latest result, based on a quarter of our anticipated final data set, sets a world-leading, model-independent limit of < 0.45 eV (90% C.L.) on the effective neutrino-mass observable from single β decay. In this talk, I will explain how KATRIN achieves its sensitivity to the neutrino-mass scale as well as the systematics control and analysis methods required to interpret its data. I will also discuss KATRIN's prospects for detecting possible signals of new physics, and its plans for the future.