Super Kamiokande or the great cathedral of science is a marvel in itself. In the February of 1987, the Kamiokande detector detected the world’s first neutrinos from a supernova burst. Since then, no supernova explosion has occurred in or near our galaxy. However, in a major revamp of Super Kamiokande, we might be closer than ever before in studying the history of supernova.
What are neutrinos?
It is a well-known fact that neutrinos are the fundamental particles that make up the entire universe that we live in and are constantly intrigued by. But the fact is, these neutrons are not understood by many. We have little idea about what they are made up of and how they work, but still, it is not certain.
Wolfgang Pauli had predicted a hypothetical particle back in 1931 that energy and momentum can not be conserved in a certain radioactive decay. The missing energy was carried by a neutral particle which escaped detection. Later in 1959, Clyde Cowan and Fred Reines, discovered a particle fitting the characteristics of the neutrino which was a partner of electrons. Two other variants of neutrons were detected in 1962 and 1978 and were named Muon neutrino and Tau neutrino respectively.
The Origin of Super Kamiokande
Therefore, in order to study neutrinos further, a Super Kamiokande was built in 1996. This giant and versatile detector is able to detect neutrinos with energies from a few Mev (megaelectron volt which is equal to electron volts) to a few hundred Gev (Gigaelectron vault which is equal to electron volts). The predecessor of Super-kamiokande was the KamiokaNDE which was the short form of Kamioka Nucleon Decay Experiment. The project started in 1982 and was completed in April 1983 at the Kamioka Observatory, the Institute for Cosmic Ray Research, University of Tokyo by Koshiba Masatoshi and Kajita Takaaki, who received a Noble Prize in Physics for their contribution in this project.
The purpose of this observatory was to detect if proton decay exists which was one of the most fundamental questions in the study of elementary particle physics. It was a tank with 16.0 m of height and 15.6 m in width. It contained 3,048 metric tons of pure water and over 1,000 photomultiplier tubes attached to its inner surface.
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After realizing that the observatory could do more than just detect proton decay, this observatory underwent an upgrade. In this upgrade they observed electrons from Muon decay that further recognized that the detectable energy of these electrons could go down to 10 MeV.
This let the physicists observe solar neutrinos in 1985 and as a result it became sensitive enough to detect the neutrinos from SN 1987A, a supernova which was observed in the Large Magellanic Cloud in February 1987. The Large Magellanic Cloud is a galaxy of satellites in the Milky Way. In 1984, at ICONBAN84 held in Park City, Utah, two presentations were made. One was a report on their latest physics results and another was a proposal to construct a 22.5 kton water Cherenkov detector called JACK (Japan America Collaboration at Kamioka) and thus Super-Kamiokande came into existence.
What does Super Kamiokande Looks Like?
When the proposal for the construction for Super Kamiokande was approved in 1991, subjects like Neutrino astronomy, Solar neutrinos and Supernova neutrinos, and Proton decay became the priority of this observatory. The Japanese Ministry of Education, Science, Sports and Culture funded approximately $100 M for this project while the US Department of Energy contributed $3 M in addition to contributing 2000 20cm PMTs recycled from the IMB experiment.
The Super Kamiokande is located 1000 m underground in the Kamioka mine, Gifu prefecture, Japan. The horizontal tunnel leads to the area of experiment through 1.7 km drive. It is a cylindrically shaped detector that is 42.2 m tall and is 39.6 m in diameter. It contains 50kton of water inside. The inner 32 kton is home to eleven thousand photomultiplier tubes which is way more than the original Kamiokande. The inner detector is surrounded by ~2 to 3 m thick water layers, viewed by 1885 PMTs of 20 cm diameter. These are used to shield and identify incoming particles in the Super Kamiokande
From Super Kamiokande To Hyper Kamiokande
The Super-K Collaboration announced the first ever evidence to prove neutrino oscillation in 1998, which was the first theory to support that neutrino has non-zero mass. As a result, in 2015, Super-K researchers Takaaki Kajita and Arthur McDonald won the Noble Prize in Physics at the Sudbury Neutrino Observatory for their work confirming Neutrino oscillation. As good as everything was going for this Super-K, on 12th November, 2001, 6,600 photomultiplier tubes imploded inside the detector. The detector was restored by adding acrylic shells to protect the photomultiplier tubes which did not implode.
The solar Neutrino study, the evidence of day/night effect need to be strengthened and detailed study on the neutrino oscillations have been going on since its discovery. Since its renovations, neither proton decay nor another neutrino bursts from supernovae were not observed. Further answers for some of the remaining problems may be found in the future but the size of the Super-K is just not big enough. Therefore, a Hyper-Kamiokande with 8 times bigger fiducial mass is being planned and is said to be ready by 2027. The researchers will use this facility to study the history of the universe and the theory of elementary particles.
The Future of Super Kamiokande and Supernova
Supernova explosions in our galaxy may be fairly rare, but supernovae themselves are not. On average, there is one core collapse supernova (ccSN) somewhere in the universe each second. The neutrinos emitted from all of these ccSN since the onset of stellar formation have suffused the universe.
The detection of the supernova relic neutrinos will enable Super Kamiokande to investigate the history of star formation, a key factor in cosmology, nucleosynthesis, and stellar evolution. Furthermore, the study of supernova bursts, which produce and disperse elements heavier than helium, is vital to understand many aspects of the present universe.
Let’s hope Super Kamiokande and Hyper Kamiokande will actually open the doors to the inception of the universe and get us closer to the galaxies than ever before.