Amazing stuff!
"In a milestone that will bear on future discoveries in nuclear and particle physics, today an international team including scientists from MIT announced that they have established a new upper limit on the mass of the neutrino subatomic particle: 0.8 eV/c2. ...
The team’s first reported measurement in 2019 yielded a result of 1.1 eV/c2. Scientists later broke the 1 eV/c2, a testament to the precision of the technique. Further measurement of the neutrino’s mass will continue through 2024.
To measure neutrino mass, KATRIN makes use of the beta decay of tritium, an unstable hydrogen isotope. The team was able to determine the mass of the neutrino via the measured energy of electrons released in the decay process. But to do so has necessitated a major technological effort: The 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.
... “[Enrico] Fermi himself devised the technique back in the 1930s. But only now do we have the capabilities to make use of the technique to extract the neutrino mass with such precision.” ...""... When a tritium nucleus transmutes into a helium one, it ejects an electron and a neutrino (or, more accurately, a particle with an equal mass called an antineutrino). The neutrino is lost, but the electron is channelled into a 23-metre-long, steel vacuum chamber shaped like a Zeppelin airship, where its energy is measured precisely.
The electron carries almost all of the energy released during the tritium’s decay, but some is lost with the neutrino. The value of this shortfall can be used to calculate the particle’s mass. ..."
From the abstract:
"Since the discovery of neutrino oscillations, we know that neutrinos have non-zero mass. However, the absolute neutrino-mass scale remains unknown. Here we report the upper limits on effective electron anti-neutrino mass, mν, from the second physics run of the Karlsruhe Tritium Neutrino experiment. In this experiment, mν is probed via a high-precision measurement of the tritium β-decay spectrum close to its endpoint. This method is independent of any cosmological model and does not rely on assumptions whether the neutrino is a Dirac or Majorana particle. By increasing the source activity and reducing the background with respect to the first physics campaign, we reached a sensitivity on mν of 0.7 eV c–2 at a 90% confidence level (CL). The best fit to the spectral data yields m2ν = (0.26 ± 0.34) eV2 c–4, resulting in an upper limit of mν < 0.9 eV c–2 at 90% CL. By combining this result with the first neutrino-mass campaign, we find an upper limit of mν < 0.8 eV c–2 at 90% CL."
A new upper limit on the mass of neutrinos Researchers with the KATRIN experiment determine that neutrinos are lighter than 0.8 eV/c2.
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