Weighing the lightest matter: Probing the absolute neutrino mass scale with direct measurements

How heavy is the lightest known particle of matter? The neutrino mass remains one of the central open questions in fundamental physics, with implications ranging from cosmology to particle theory.  While neutrino oscillation studies provide precise measurements of mixing parameters and mass-squared differences, determining the absolute neutrino mass scale requires a different experimental strategy. Direct kinematic measurements of weak decays offer a unique, model-independent approach to this challenge. In recent years, the field has entered a new era: advances in detector technology have enabled significant progress in calorimetric measurements of electron capture in holmium-163, while novel frequency-based techniques have been developed to probe the β-spectrum of tritium. At present, the KATRIN experiment represents the worldʼs leading effort, employing a high-intensity gaseous tritium source and a high-resolution electrostatic spectrometer. It has now achieved a sensitivity of 0.45 eV/c² and continues to accumulate data.

In this talk, I will review the current landscape of direct neutrino-mass searches, highlight recent milestones from both tritium- and holmium-based efforts, and discuss the outlook for pushing the frontier even further in the coming years.