Super-Kamiokande

On this day in 1996, the Super-Kamiokande experiment began searching for neutrinos in the Kamioka mine in Japan. Neutrinos are uncharged subatomic particles that come in three varieties and rarely interact with other matter. To find them, Super-Kamiokande is filled with 50,000 metric tons of water and 13,000 light sensors. The sensors pick up the flashes of light generated when neutrinos strike atoms in the water. In 1998, researchers led by Takaaki Kajita presented evidence from Super-Kamiokande suggesting that neutrinos can morph from one variety, or flavor, into another. The discovery proved that neutrinos have mass, even though prevailing theories had predicted the particles would be massless. Kajita won a share of the 2015 Nobel Prize in Physics. As this photo shows, Super-Kamiokande is also one of the most impressive settings for science you’ll ever see. [Photo credit: Kamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyo]

Date in History: 1 April 1996