Katrin
KATRIN is a German acronym (Karlsruhe Tritium Neutrino Experiment) for an undertaking to measure the mass of the electron antineutrino with sub-eV precision by examining the spectrum of electrons emitted from the beta decay of tritium. The core of the apparatus is a 200-ton spectrometer. In 2015, the commissioning measurements on this spectrometer were completed, successfully verifying its basic vacuum, transmission and background properties. The experiment began running tests in October 2016, with measurements scheduled in 2017.
The spectrometer was built by MAN DWE GmbH in Deggendorf. Although only 350 km from Karlsruhe, the tank's size made land transport impossible. Instead, it was shipped by water, down the Danube to the Black Sea, through the Mediterranean Sea and Atlantic Ocean to Antwerp, then up the Rhine to Karlsruhe. This 8600 km long detour limited land travel to only the final 7 km from the Leopoldshafen docks to the laboratory.
The construction proceeded well with several of the major components on-site by 2010. The main spectrometer test program was scheduled for 2013 and the complete system integration for 2014. The experiment is located at the former Forschungszentrum Karlsruhe, now Campus Nord of the Karlsruhe Institute of Technology.
The beta decay of tritium is one of the least energetic beta decays. The electron and the neutrino which are emitted share only 18.6 keV of energy between them. KATRIN is designed to produce a very accurate spectrum of the numbers of electrons emitted with energies very close to this total energy (only a few eV away), which correspond to very low energy neutrinos. If the neutrino is a massless particle, there is no lower bound to the energy the neutrino can carry, so the electron energy spectrum should extend all the way to the 18.6 keV limit. On the other hand, if the neutrino has mass, then it must always carry away at least the amount of energy equivalent to its mass by E = mc2, and the electron spectrum should drop off short of the total energy limit and have a different shape.
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