KATRIN

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The spectrometer was built by MAN DWE GmbH in Deggendorf. Although only 350 km from Karlsruhe, the tank's size made land transport impossible.[https://www.katrin.kit.edu/213.php KATRIN Main Spectrometer] Accessed 14 November 2016 Instead, it was shipped in autumn 2006 by water, down the Danube to the Black Sea, through the Mediterranean Sea and Atlantic Ocean to Rotterdam, 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.{{Cite journal |last=Thümmler |first=T. |display-authors=etal |collaboration=KATRIN collaboration |year=2010 |title=Introduction to direct neutrino mass measurements and KATRIN |journal=Nuclear Physics B: Proceedings Supplements |volume=229-232 |pages=146–151 |arxiv=1012.2282 |bibcode=2012NuPhS.229..146T |doi=10.1016/j.nuclphysbps.2012.09.024|s2cid=118585897 }} The experiment is located at the former Forschungszentrum Karlsruhe, now Campus Nord of the Karlsruhe Institute of Technology.

File:KATRIN Spectrum.svg

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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 mass-energy equivalence, and the electron spectrum should drop off short of the total energy limit and have a different shape.

In most beta decay events, the electron and the neutrino carry away roughly equal amounts of energy. The events of interest to KATRIN, in which the electron takes almost all the energy and the neutrino almost none, are very rare, occurring roughly once in a trillion decays. In order to filter out the common events so the detector is not overwhelmed, the electrons must pass through an electric potential that stops all electrons below a certain threshold, which is set a few eV below the total energy limit. Only electrons that have enough energy to pass through the potential are counted.

First results from the first measurement campaign (10 April – 13 May 2019) were published 13 September 2019. They put the upper bound of electron neutrino mass to 1.1 eV.{{Cite journal |doi = 10.1038/d41586-019-02843-7 |pmid = 31554997 |title = Neutrinos, flu vaccines and Fukushima ruling |journal = Nature |volume = 573 |issue = 7775 |pages = 468–469 |year = 2019 |bibcode = 2019Natur.573..468. |doi-access = free}}{{cite conference |url=http://www-kam2.icrr.u-tokyo.ac.jp/indico/event/3/contribution/27/material/slides/0.pdf |conference=16th International Conference on Topics in Astroparticle Physics and Underground Physics (TAUP) |place=Toyama, JP |date=9–13 September 2019 |via=U. Tokyo |title=Direct neutrino mass measurement |first1=Guido |last1=Drexlin |display-authors=etal |type=plenary talk slides |access-date=9 October 2021 |archive-date=25 December 2021 |archive-url=https://web.archive.org/web/20211225190439/http://www-kam2.icrr.u-tokyo.ac.jp/indico/event/3/contribution/27/material/slides/0.pdf |url-status=dead }}

As of September 2019, the experiment hopes to achieve 3 measuring campaigns, each comprising 65 days of active measurement, in a year. The experiment reckons it needs 1000 days of measurement to reach target sensitivity of 0.2 eV (upper limit for neutrino mass). Thus the final results are expected in 5–6 years.

The February 2022 upper limit is m_ν < 0.8 eV c^–2 at 90% CL in combination with the previous campaign.

The precise mass of the neutrino is important not only for particle physics, but also for cosmology. The observation of neutrino oscillation is strong evidence in favor of massive neutrinos, but gives only a weak lower bound.{{cite journal |last1=Angus |first1=G. W. |last2=Shan |first2=H. Y. |last3=Zhao |first3=H. S. |last4=Famaey |first4=B. |year=2007 |title=On the Proof of Dark Matter, the Law of Gravity, and the Mass of Neutrinos |journal=The Astrophysical Journal Letters |volume=654 |issue=1 |pages=L13–L16 |arxiv=astro-ph/0609125 |bibcode= 2007ApJ...654L..13A |bibcode-access=free |doi=10.1086/510738 |doi-access=free }}

Along with the possible observation of neutrinoless double beta decay, KATRIN is one of the neutrino experiments most likely to yield significant results in the near future.

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• [http://www.katrin.kit.edu/ KATRIN homepage]
• [https://web.archive.org/web/20110721190135/http://www.szczepanek.de/~kathrin/mainspec_arrival.html Arrival of KATRIN main spectrometer at Karlsruhe (pictures)]
• [http://inspirehep.net/record/680949/ KATRIN design report 2004]
• [https://inspirehep.net/experiments/1108400 KATRIN experiment] record on INSPIRE-HEP

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Category:CERN experiments