-Manasi Jalindar

The Super-Kamiokande (short for Super Kamioka Neutrino Detection Experiment), located in Hida, Gifu Prefecture, Japan, is a neutrino observatory. Built in 1991, the observatory is the successor of the KamiokaNDE. With a total funding of $100 M, Super-Kamiokande operations began in 1996.

The KamiokaNDE (Kamioka Nucleon Decay Experiment) was successful in neutrino astronomy and astrophysics, but could not detect proton decay due to its low sensitivity. To serve this purpose, a proposal was made to build a water cherenkov detector JACK(Japan America Collaboration at Kamioka), which was later named Super-K.

It is the world’s largest Cherenkov detector, operated in collaboration between Japan and the US. Located 1000m below the ground, Super-Kamiokande is about 40 metres high, 39 metres in diameter, containing 50,000 tons of ultrapure water (which can dissolve metal!). The surface inside is covered by 13,000 photomultiplier tubes PMT (converts faint light to electric current) used to detect Cherenkov radiation, which produces a ring on the detector wall. To protect the PMTs from radiation, the cavity roof and access tunnels are sealed with Mineguard coating.

In 1998, Super-K provided the very first evidence of neutrino oscillations, which supports the theory that a neutrino has a non-zero mass. This gained Takaaki Kajita and Arthur Mcdonald the Nobel Prize in 2015.

Super-K has used pure water for decades. In 2019, gadolinium was added to make it more sensitive to antineutrino. The project was termed as SK-Gd Project.

Other major experiments conducted were K2K and T2K experiments. K2K (KEK to Kamioka)(1999-2004) was conducted to verify neutrino oscillations through muon neutrinos. The T2K experiment (Tokai to Kamioka) was a collaboration between several countries to gain deeper insights into neutrino oscillations. They announced their results in 2011. Moreover, research on solar and atmospheric neutrinos also takes place here.

The observatory has 3 monitoring systems, namely Online Monitoring System, which monitors the event data, Realtime Supernova Monitor which can detect the bursts from supernova explosions and Slow Control Monitor to give alerts. On November 10, 2001, a catastrophe occurred when more than 11,000 PMTs were destroyed in a chain reaction. One of the leading researchers believes that the imploding was due to the purity of water.

As of 2018, the experiment has around 175 researchers from 44 institutions over 10 countries. The Japanese government has now approved to build a new detector - Hyper Kamiokande - containing five times more water and four times more PMTs than Super-K. Aimed to start in 2027, this project will be used to detect proton decay and difference between neutrino and antineutrino.

References:

https://lh3.googleusercontent.com/-IbdoMWnDeNQ/VbYX8zW8DcI/AAAAAAABEmE/0bnuDhsZ-0U/super-kamiokande-3%25255B6%25255D.jpg?imgmax=1200

https://www.symmetrymagazine.org/sites/default/files/images/standard/Inline1_Super_K_Upgrade.png

https://photonterrace.net/en/adventure/vol_02/file/388/sk-en.jpg

https://www.researchgate.net/profile/James-Stewart-18/publication/45863929/figure/fig4/AS:306079742349315@1449986505134/Two-simulated-events-displayed-for-the-Super-Kamiokande-detector-Left-a-muon-event.png

https://sites.slac.stanford.edu/neutrino/sites/neutrino.sites.slac.stanford.edu/files/t2k-crosssection.png