Mass of electron neutrino11/30/2022 ![]() ![]() Until about two decades ago, neutrinos - which were theoretically predicted in 1930 and discovered in 1956 - were presumed to be massless. ![]() “Depending on what the mass of the neutrino turns out to be, it may lead to very exciting times in cosmology,” said Diana Parno, a physicist at Carnegie Mellon University and a member of the KATRIN team. Its measured mass would also serve as a check on cosmologists’ theories for how the universe evolved. Measuring its mass would help point toward new laws of physics beyond the Standard Model, the remarkably successful yet incomplete description for how the universe’s known particles and forces interact. The neutrino is the only known particle whose mass remains a mystery. Mass is one of the most basic and important characteristics of fundamental particles. As its data accrues, KATRIN aims to nail the actual mass rather than giving an upper bound. This initial estimate, from only one month’s worth of data, improves on previous measurements using similar techniques that placed the upper limit on the neutrino mass at 2 eV. And in September, after 18 years of planning, building and calibrating, the Karlsruhe Tritium Neutrino (KATRIN) experiment in southwestern Germany announced its first results: It found that the neutrino can’t weigh more than 1.1 electron-volts (eV), or about one-five-hundred-thousandth the mass of the electron. Physicists have long tried to weigh the ghost. “The fact that they’re ubiquitous, yet we don’t even know what they weigh, is kind of crazy,” said Deborah Harris, a physicist at the Fermi National Accelerator Laboratory near Chicago and York University in Toronto. About a thousand trillion of the ghostly particles pass through your body every second - with nary a flinch from even a single atom. Despite their abundance, however, neutrinos are hard to catch and inspect, as they interact with matter only very weakly. Of all the known particles in the universe, only photons outnumber neutrinos. ![]()
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