New Kamland Proton Decay Search

The Kamland-Zen collaboration has a new preprint on the arXiv on searching for proton decay to a kaon and an antineutrino. Kamland is a detector based at the Kamioka underground lab in the mountains of Japan. It consists of a spherical volume filled with liquid scintillator and uses photomultiplier tubes to measure events happening in the detector volume.

This decay mode is found in various grand unified theories and in the Standard Model is kinematically allowed but cannot happen due to conservation of baryon number and lepton number. If a unified theory conserves some combination of these quantum numbers but not all of them separately, then it can allow for such exotic phenomena to occur. Enough energy is released by the decay that radioactive backgrounds are basically irrelevant. Kaons can be produced in neutrino interactions but these events should be rare.

They find a limit on proton decay if it occurs through this channel of greater than 1032 years. This is still behind the best SuperK result, but SuperK has also been running for a lot longer than Kamland and has a much bigger detector. The Kamland-Zen group seems to see this as more of a proof of principle work showing that large scintillator detectors are useful at looking for rare events like proton decay.