What Does a Neutrino Weigh? – That is not yet known. But we do know that they are the lightest of all the subatomic particles that have mass. And that a direct measurement of their mass could make an important contribution to cosmological structure formation models.
The team at the Karlsruhe Tritium Neutrino Experiment (KATRIN) in Germany took a step forward in February 2022. For the first time, they were able to detect the maximum mass of a neutron in a measurement and found that neutrinos have a maximum mass of 0.8 eV/c². [1]
What Is a Neutrino?
Neutrinos are electrically neutral and one of the fundamental particles, which means a neutrino is not made of any smaller pieces, at least that we know of.
In the standard model of elementary particle physics, three types (generations) of neutrinos exist: Electron neutrinos, muon neutrinos, and tau neutrinos. Each neutrino generation consists of the neutrino itself and its anti-neutrino.
The name neutrino was proposed by Enrico Fermi (1901 – 1954) for the particle postulated by Wolfgang Pauli (1900 – 1958). The name is composed of the Italian diminutive ino and neutrum, Latin for neutral. [2]
How Was the Maximum Mass Measured?
Neutrinos are the most abundant massive particles in the universe. They are created, for example, by the decay of heavier particles. The most direct way to assess the neutrino mass is via the kinematics of single-β decays or electron capture processes:
When a tritium nucleus decays into a helium nucleus, it ejects an electron and an antineutrino.
At the KATRIN experiment, the neutrino is lost, but the electron is passed into a 23-meter steel vacuum chamber. A system of superconducting magnets guides the electrons from the source into the spectrometer area and to the focal detector. There, its energy is accurately measured. The difference between the energy of the decay and the electron is used to calculate the mass of the neutrino.
According to the researchers, their experiment is the only one in the world that also allows a definitive measurement of the neutrino’s mass. However, if the mass is less than 0.2 eV, it could be outside the sensitivity of the experiment. They hope to have results after complete data collection in 2024. The search for the exact mass remains exciting.
Reference
[1] The KATRIN Collaboration, Direct neutrino-mass measurement with sub-electronvolt sensitivity, Nat. Phys. 2022, 18, 160–166. https://doi.org/10.1038/s41567-021-01463-1
[2] Kai Zuber, Neutrino Physics, CRC Press Inc., Boca Raton, FL, USA, 2011. ISBN: 978-1-4200-6471-1
Corrigendum (May 13, 2024):
The text originally said,
Also of Interest
- What is a Yoctosecond? – How many yoctoseconds are in a second?
- What is a Baryon? – Any idea?
