LOS ANGELES — For the first time, physicists have confirmed that certain subatomic particles have mass and that they could account for a large proportion of matter in the universe, the so-called dark matter that astrophysicists know is there but that cannot be observed by conventional means.
The finding concerns the behavior of neutrinos, ghost-like particles that travel at the speed of light. In the new experiment, physicists captured a muon neutrino in the process of transforming into a tau neutrino.
Researchers had believed that such transformations occur because they have observed the disappearance of muon neutrinos in a variety of experiments. But the research announced Monday marks the first time the appearance of a tau neutrino has been directly observed.
The new finding is important because it will require a reworking of the theories now used to explain the behavior of fundamental particles.
