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KATRIN

KATRIN is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand KATRIN rather than just read about it. In short: 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 experiment is a recognized CERN experiment (RE14).

KATRIN — main illustration
KATRIN — illustration

Key takeaways

  • KATRIN belongs to science; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect KATRIN to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of KATRIN from memory before moving on to harder problems.

Reference excerpt

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 experiment is a recognized CERN experiment (RE14). 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. The inauguration took place 11 June 2018, with the first tritium measurements by the experiment (the so-called First Tritium or FT 2-week engineering run in mid-2018). The projected experiment duration at the time was 5 years. The first science measurements (so-called first campaign) took place 10 April 2019. In February 2022, the experiment announced an upper limit of mν < 0.8 eV c–2 at 90% confidence level. In April 2025 this result was improved to mν < 0.45 eV c–2 at the same confidence level.

Construction and assembly

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 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. The experiment is located at the former Forschungszentrum Karlsruhe, now Campus Nord of the Karlsruhe Institute of Technology.

Experiment

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 = m c ², 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.

Results 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. 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 mν < 0.8 eV c–2 at 90% CL in combination with the previous campaign. In April 2025, this result was improved to mν < 0.45 eV c–2 at the same confidence level (using the 2019–2021 dataset).

Importance 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. 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.

External links

KATRIN homepage Arrival of KATRIN main spectrometer at Karlsruhe (pictures) KATRIN design report 2004 KATRIN experiment record on INSPIRE-HEP

References

Illustrations

KATRIN: Transport of the main spectrometer to the Karlsruhe Institute of Technology.
Transport of the main spectrometer to the Karlsruhe Institute of Technology.
KATRIN: Illustration of KATRIN beamline and its main components.[5]
Illustration of KATRIN beamline and its main components.[5]
KATRIN: Energy spectrum of the electrons emitted in tritium beta decay. Three graphs for different neutrino masses are shown. These graphs differ only in the range near the high-energetic end-point; the intersection with the abscissa depends on the neutrino mass. In the KATRIN experiment the spectrum around this end-point is measured with high precision to obtain the neutrino mass.
Energy spectrum of the electrons emitted in tritium beta decay. Three graphs for different neutrino masses are shown. These graphs differ only in the range near the high-energetic end-point; the intersection with the abscissa depends on the neutrino mass. In the KATRIN experiment the spectrum around this end-point is measured with high precision to obtain the neutrino mass.
KATRIN: Timeline of neutrino mass measurements by different experiments.[5]
Timeline of neutrino mass measurements by different experiments.[5]

Worked examples

Example 1 — a first encounter with KATRIN

Start with the simplest possible case. Write down what KATRIN claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to KATRIN before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about KATRIN ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of KATRIN

In research
KATRIN appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses KATRIN in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
KATRIN is common in secondary-school and first-year university syllabi. It links to neighbouring topics CERN experiments, Neutrino experiments, so understanding it makes those chapters shorter.
In everyday life
Look for KATRIN outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study KATRIN in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what KATRIN means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain KATRIN out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is KATRIN in simple terms?

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 experiment is a recognized CERN experiment (RE14).

Why does KATRIN matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study KATRIN?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on KATRIN.

Tags

  • CERN experiments
  • Neutrino experiments

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