Scientists still don’t understand why neutrinos are abnormally light ( SN: 2/26/18). In the coming years, additional data should further squeeze the neutrino’s maximum possible bulk.

That’s because mass and energy are two sides of the same coin a more massive neutrino would mean less energy could go to the electron in the decayĪ previous estimate from KATRIN, using a smaller amount of data, found that the neutrino’s mass was less than 1.1 electron volts ( SN: 9/18/19). Measuring the energies of the electrons can reveal the masses of the antineutrinos that flitted away. The KATRIN experiment studies tritium, a rare form of hydrogen that decays radioactively, emitting an electron and an antimatter mirror image of the neutrino, an antineutrino. “Neutrino masses are tiny,” said Parno, of Carnegie Mellon University in Pittsburgh. The first clear experimental evidence for the difference between electron and muon neutrinos came from an experiment conducted at Brookhaven in 1962. For comparison, electrons are more than 600,000 times as bulky, at about 511,000 electron volts. Tau neutrinos are not detected by these detectors because the neutrino energies are not sufficient to produce tau particles (which are about 3500 times the mass of an electron). The puny particles have masses of 0.8 electron volts or less, physicist Diana Parno reported April 19 at a virtual meeting of the American Physical Society. A new estimate from the KATRIN experiment, located in Karlsruhe, Germany, further shrinks the maximum possible mass neutrinos could have. But scientists still don’t know exactly how slight the particles are. They’re a tiny fraction of the mass of the next lightest particle, the electron. The subatomic particles are so lightweight, they’re almost massless. To understand neutrinos, it pays to be small-minded.

Electron neutrino mass