Scientists use the near detector to verify the intensity and purity of the muon neutrino beam leaving the Fermilab site. | Courtesy of Fermilab, photo by Peter Ginter
Blink! The split-second choice: Each of us makes them, but how much of a difference do they really make? If you’re a tiny particle known as a neutrino, those instant decisions might add up, and make all the difference in the world . . . and the universe.
Neutrinos are among nature’s most abundant, but least-visible actors. Virtually without mass and carrying no electrical charge, they flit across the stage of the universe at nearly the speed of light, barely interacting with any of the other actors as they pass through them, whether stars or planets or people.
But those same ghostly particles -- trillions of which are passing through you right now -- could actually be clues that help explain why there are people . . . and planets . . . and stars. And it would be related to the neutrino’s ability to change not just their minds, but their entire identities, in the blink of an eye.
In a sense, this story began at the Energy Department’s Brookhaven National Laboratory in 1962. That’s where a group of scientists detected that there was more than one type, or flavor, of neutrino. They received the 1988 Nobel Prize in Physics for their discovery of the muon neutrino. Other scientists had already discovered another flavor, the electron neutrino. And the discovery of the third and final flavor of neutrino, the tau, was announced at Illinois’ Fermi National Accelerator Lab in 2000.
For the last six years, researchers at Fermilab have been studying neutrinos and how they might change, or oscillate, between their three different identities via an experiment known as MINOS (the Main Injector Neutrino Oscillation Search). In the experiment, a beam of muon neutrinos is created at Fermilab and sent through solid earth some 450 miles to a 5,000-ton detector located half-a-mile below the ground in Minnesota’s Soudan Underground Laboratory. The trip takes the blink of an eye -- about four-hundredths of a second -- which is more than enough time for them to change their minds and switch their identities.
These changing events are rare, but scientists are quite certain they happen. In fact, Fermilab scientists recently (June 24th, 2011) announced that they have seen candidates for muon neutrinos changing into electron neutrinos.
The finding is significant for two reasons. First, it’s consistent with a finding announced earlier this month (June 15th) by Japan’s T2K experiment, which also showed evidence of muon neutrinos changing into electron neutrinos. Second, if these rare transformations hold true, if muon neutrinos do change into electron neutrinos, it could be the reason that we’re surrounded by stars . . . and planets . . . and people.
Scientists believe that in the beginning of the universe (the big bang), the amounts of matter and antimatter were equal. However, most of what we see around us is matter. The neutrino’s ability to change identities instantly could be a great part of the reason why some matter remained, even as the antimatter was annihilated.
That’s why Fermilab scientists are continuing to study the elusive neutrino and its sudden transformations. In fact, they’re leading a collaboration of some 180 scientists and engineers from some 28 institutions in a new experiment called NOvA. The scientists will analyze the phenomena in more detail to discover more about the tiny masses that neutrinos have, which will help them better understand the evolution of the early universe.
It’s worth considering the next time you’re faced with sudden choice: A tiny particle . . . an instant decision . . . and an immense difference.
For more information on the Department's Office of Science, please go to: http://science.doe.gov/.