Phantom Filter
Super Kamiokande detector
Buried 1000 meters under the city of Hida, Japan, and packed with 11,146 photomultiplier tubes, the Super Kamiokande detector is set up to capture the presence of what may be the universe’s most bashful particle. The ghost-like neutrino has no electrical charge and a near zero mass. That means it doesn’t like to play with most other particles. No, the shy “little neutral one,” as the translation of neutrino from Italian goes, prefers to stick to itself. In fact, neutrinos sail right through all that rock over Super Kamiokande and leave most of the interacting particles that accompanied them on their journey through space to face plant in the dirt. With most of the excess noise from other particles filtered out above, researchers just have to wait for neutrinos to slip through the ceiling and dive into the detector’s 50,000-ton water tank (pictured here empty).
Despite their Olympic-caliber dive in, neutrinos do occasionally bump into an H2O molecule in the tank. The splash results in the release of a charged particle, either an electron or muon. Those particles shoot out from the neutrinos’ rare belly flops faster than the speed of light, in water, in which light travels more slowly than it does through the emptiness of space. The result of breaking that aquatic speed limit is the creation of a subtle cone of light, a kind of optical sonic boom. It’s this light cone that all those silver photomultipliers on the walls were installed to detect, and all sorts of information can be gathered by analyzing the cone’s precise shape. Astronomers have used the detector to see deep into our sun, collapsed stars, and the center of our galaxy.
Tags: electron, muon, neutrino, particles, photomultiplier
