KATRIN: First Tritium measurements

The KATRIN experiment aims at measuring the effective electron antineutrino mass with a 0.2 eV (90% C. L.) sensitivity by analysing the $\beta$-decay spectrum of molecular tritium near its endpoint. In May and June 2018, the KATRIN collaboration took its first commissioning data using a gaseous tritium source. These low activity data have been used to test the stability of the entire apparatus – from the windowless gaseous source to the focal plane detector – to the 0.1% level. In addition, these first commissioning runs have been successfully utilised to test the KATRIN model and ensure the reproducibility of the fitting results, which are presented in this document. In March 2019, KATRIN entered the neutrino mass measurement phase, taking high activity tritium runs