Welcome to Super-Kamiokande!

One of Super-Kamiokande’s (Super-K) main research topics is the “neutrino.” Neutrinos are a type of elementary particle, like electrons and quarks, but since they have no electric charge they interact with matter only very rarely. For this reason a large amount of material is needed to detect them and this is why the Super-K tank holds 50,000 tons of ultra-pure water. Though it was once believed that neutrinos do not have mass, Super-K’s discovery of neutrino oscillations (a phenomena in which neutrinos change their type) revealed that they are in fact massive. This experimental breakthrough illustrated that the standard model of elementary particles is incomplete and opened the door for future models.

Since neutrinos interact only weakly with matter they can be used to investigate both the deep interior of stars and the far reaches of the universe. For example, we can observe not only the core of our sun, whose nuclear fusion creates the light that powers the Earth, but also the moment when the central core of a massive star collapses as a supernova burst using the neutrinos these processes create. In addition, the neutrinos from all supernovae that have occurred since the beginning of the universe are flying all around us today and we can use these “relic” neutrinos to study the history of the universe.

Another important research topic at Super-K is the search for proton decay. If the proton is the lightest member of its particle family, the law of conservation of energy prohibits it from decaying. However, if, for example, electrons, neutrinos, and pions are all members of the proton family, it would be possible for the proton to decay and produce them since they are all lighter particles. Observing the decay of a proton would verify that these particles are part of the same family and thereby provide direct evidence for Grand Unified Theories, a class of theories which extend the standard model of elementary particles.

Since August 2020, the rare earth element gadolinium has been introduced into the SK detector, starting a new period of observations. The addition of gadolinium improves SK’s ability to observe neutrinos and enables the first ever observation of “supernova relic neutrinos”(SRNs). SRNs are produced by many supernova explosions occurred since the beginning of the universe. So, we should be able to investigate the history of the universe through the observation of SRNs.

Finally, I would like to thank you for your interest in Super-K and ask that you keep watching for our future results.

Masayuki Nakahata