While the oft-troubled Large Hadron Collider is starting back up today after a weekend glitch, another big physics project is under way halfway around the world. The British and Japanese researchers behind the project called T2K (Tokai-to-Kamioka) announced their first neutrino detection, the initial step in an experiment to understand these mysterious subatomic particles.
Neutrinos are tiny particles that rarely interact with matter, making them incredibly difficult to study. But physicists have done it by looking for the signature left behind when one of the torrent of neutrinos flying through the Earth at any given time happens to crash into the nucleus of an atom within view of a neutrino detector. Japan’s Super Kamiokande is one of the largest neutrino detectors, and now it has a new mission under the T2K project. The goal is to understand a strange kind of subatomic metamorphosis. These particles come in three types or flavours: electron, muon and tau neutrinos. From earlier experiments, physicists know that neutrinos spontaneously change their flavour, oscillating back and forth from one kind to another. But the details are still hazy [New Scientist].
To study this, the scientists are creating their own stream of neutrinos at a facility near the town of Tokai north of Tokyo. That beam is aimed at the Super Kamiokande in Kamioka (thus the name Tokai-to-Kamioka), and travels about 185 miles to get there. The Super-Kamiokande detector is buried in an old zinc mine 3,250 feet under Mt. Ikena near Kamioka in the Japanese Alps. The massive cylindrical detector contains 12.5 million gallons of ultra-pure water and is lined with an acre of photomultiplier tubes, which detect light from neutrino collisions and convert it into an electrical signal [Los Angeles Times].
And beyond the fact that chasing ghost particles with water tanks built in an abandoned mine is just plain cool, team member David Wark says his grander hope is that the study has something to say about the antimatter-matter question. That is, why do we live in a universe dominated by matter, instead of one where antimatter and matter annihilated each other after the Big Bang? “That tells us there must be a law of physics that is different for matter and antimatter. We don’t know what it is, but neutrino oscillations are someplace where it might show up” [New Scientist], he says.
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Image: Super Kamiokande