'Only by this laborious and intricate method we were able to exclude a systematic bias of our result due to distorting processes. Each and every effect, no matter how small, had to be investigated in detail. The in-depth analysis of this data was demanding everything from the international analysis team led by its two coordinators, Susanne Mertens (Max Planck Institute for Physics and TU Munich) and Magnus Schlösser (KIT). Christian Weinheimer (University of Münster), the other co-spokesperson, adds that 'the increase of the signal rate and the reduction of background rate were decisive for the new result.' 'KATRIN is an experiment with the highest technological requirements and is now running like perfect clockwork' enthuses Guido Drexlin (KIT), the project leader and one of the two co-spokespersons of the experiment. The high quality of the data after starting scientific measurements in 2019 has continuously been improved over the last two years. This necessitates a major technological effort: the 70 meter long experiment houses the world´s most intense tritium source as well as a giant spectrometer to measure the energy of decay electrons with unprecedented precision.

It makes use of the beta decay of tritium, an unstable hydrogen isotope, to determine the mass of the neutrino via the energy distribution of electrons released in the decay process. This is the challenge the international KATRIN experiment at Karlsruhe Institute of Technology (KIT) with partners from six countries has taken up as the world´s most sensitive scale for neutrinos. Without a measurement of the mass scale of neutrinos our understanding of the universe will remain incomplete.

In cosmology they play an important role in the formation of large-scale structures, while in particle physics their tiny but non-zero mass sets them apart, pointing to new physics phenomena beyond our current theories. Neutrinos are arguably the most fascinating elementary particle in our universe.

Electron neutrino mass