Physicists Get Close to Knowing the Mass of the Neutrino

Wired | 10/27/2019 | Staff
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Of all the known particles in the universe, only photons outnumber neutrinos. Despite their abundance, however, neutrinos are hard to catch and inspect, as they interact with matter only very weakly. About 1,000 trillion of the ghostly particles pass through your body every second—with nary a flinch from even a single atom.

Original story reprinted with permission from Quanta Magazine, an editorially independent publication of the Simons Foundation whose mission is to enhance public understanding of science by covering research develop­ments and trends in mathe­matics and the physical and life sciences.

Fact - Kind - Crazy - Deborah - Harris

“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.

Physicists have long tried to weigh the ghost. 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.

Estimate - Month - Worth - Data - Improves

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. As its data accrues, KATRIN aims to nail the actual mass rather than giving an upper bound.

Mass is one of the most basic and important characteristics of fundamental particles. The neutrino is the only known particle whose mass remains a mystery. 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. Its measured mass would also serve as a check on cosmologists’ theories for how the universe evolved.

Mass - Neutrino

“Depending on what the mass of the neutrino turns out...
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