Super-K Restarts

About a year after an accident stopped the world’s largest neutrino detector in its tracks, Super-Kamiokande in Japan is on schedule to start up again in January. The surviving photomultiplier tubes in the central detector have been redistributed and enclosed in individual protective casings to prevent a repeat of the chain reaction that popped some 7000 PMTs (see Physics Today, January 2002, page 22 ). The detector will run at about half its original density—which reduces its sensitivity to low-energy solar neutrinos—for a few years, until the made-to-order 50-cm detectors can be replaced. The $20 million for these repairs is expected to be covered by Japan’s Ministry of Education, Culture, Sports, Science and Technology. The full restoration of the smaller, outward-facing PMTs that monitor the coaxial outer detector was paid for with about $2 million from the US Department of Energy.

Refilling the detector with 50 000 tons of water is slated to be completed by mid-December. Super-K is already keeping an eye out for neutrinos from supernovas. In January, an experiment to look for neutrino oscillation using a manmade beam from the KEK proton accelerator 250 kilometers away in Tsukuba will resume.