Neutrinos' maximum possible mass shrinks further

Neutrinos are known to have tiny masses. A new result proclaims the subatomic particles to be even tinier still. The electrically neutral particles, produced in radioactive decays and in reactions in the sun and elsewhere in the cosmos, have a mass of less than 0.45 electron volts, physicists report in the April 11 Science. The result, from the Karlsruhe Tritium Neutrino, or KATRIN, experiment slashes the experiment’s previous upper limit for neutrino mass by nearly half. Sign up for our newsletter We summarize the week's scientific breakthroughs every Thursday. Neutrinos are the only class of fundamental particle for which the mass, one of the most basic attributes of any particle, is unknown. The particles are so much lighter than others that they were long thought to have no mass at all. Now, one of the major puzzles in particle physics is understanding why neutrinos are so lightweight — less than a millionth the mass of an electron. Measuring their masses would be a step toward ... Read full article.