Narrator: This is Science Today. Physicists have recently zeroed in on the first direct evidence of an elusive particle of matter called the tau neutrino. Phillip Yager, a professor of physics at the University of California, Davis, says every minute trillions of these particles float through our bodies at nearly the speed of light. But because they have no charge, they can't interact electromagnetically and therefore, leave no trace. So how did the physicists detect them? Yager, who took part in the experiment, explains.
Yager: In these experiments, there's something called triggering, which is to say, you don't just record everything that happens, you try to find things that have a signature that's of interest.
Narrator: In this case, the researchers used a huge particle accelerator to detect the signature left by particles called tau leptons, which are partners of the tau neutrino.
Yager: The tau lepton itself is massive enough so that when it explodes, it kicks things out sideways. And so we triggered on that using electronic means to detect the particles, just like a Geiger counter can detect a passage of radioactive particle.
Narrator: For Science Today, I'm Larissa Branin.