Kathrin Valerius – Status and prospects of direct neutrino mass searches: News from KATRIN and outlook on future projects

Precision measurements of the kinematics of weak decays offer the only model- independent (direct) approach to investigate the absolute neutrino mass scale in a laboratory experiment.

In this talk I will review the status of direct neutrino mass searches based on beta decay of tritium and electron capture in ¹⁶³Ho and give an overview of future experiments. The currently most mature technique relies on the spectroscopy of tritium beta decay near its kinematic endpoint at 18.6 keV. The KArlsruhe TRItium Neutrino experiment (KATRIN) is targeted at improving the sensitivity of this method by an order of magnitude to 200 meV/c² (90% C.L.). To this end, KATRIN utilises an ultra-luminous windowless gaseous tritium source and a high-resolution electrostatic spectrometer. In its recent „First Light“ campaign, KATRIN has successfully inaugurated its full 70-m electron beam line and is now carrying out final commissioning works leading up to the start of tritium measurements.

At the same time, novel approaches studying the electron capture spectrum in ¹⁶³Ho with cryogenic microcalorimeters (notably, ECHo, HOLMES, and NuMECS), or developing innovative techniques for tritium beta spectroscopy using radio-frequency detection of single electrons (Project 8) are gaining momentum. Experiments exploiting these new techniques are currently in the conceptual design and prototype characterisation phases, with the aim of developing these complementary methods further towards a sub-eV sensitivity on the neutrino mass.