By Peter Weiss
Physicists have found the first direct evidence for the last of the 12 subatomic particles considered the fundamental building blocks of matter. A research team from the United States, Japan, Korea, and Greece has unveiled four sets of particle tracks that it attributes to the long-sought tau neutrino.
Elusive bits of matter with no charge and little or no mass, neutrinos interact extremely rarely with other matter, making them very difficult to detect. Until now, experimenters could find only hints of tau neutrinos’ presence, such as energy and momentum missing from decays of the particle called a tau lepton. Nonetheless, scientists haven’t doubted the existence of the tau neutrino, also known as nu tau. It’s part of the framework of the so-called standard model of particle physics.