KATRIN: Directly probing neutrino mass via tritium beta decay

The KArlsruhe TRItium Neutrino experiment (KATRIN) is designed to probe the effective electron anti-neutrino mass to a projected sensitivity of 0.2 eV at the 90% confidence level. State-of-the-art technology developed by the collaboration will perform ultrahigh precision measurements of the tritium beta-decay spectrum endpoint, where the neutrino mass can be determined from the spectral shape. Molecular tritium decays in a high-luminosity windowless gaseous tritium source ahead of a magnetic guided transport system that takes the beta-electron while eliminating the backgrounds of neutral and ionic tritiums. The kinetic energy of the beta-electrons can then be measured to high-resolution by the large (10 m diameter) spectrometer that uses the MAC-E-filter design. KATRIN have started commissioning runs, including a first tritium run, with the goals of demonstrating subsystem performance and understanding systematics. This talk will give an overview of the experiment and its challenges; some of the commissioning results will also be presented.