World's Largest Neutrino Detector, Hyper-K, Has Been Given The Go-Ahead

The Japanese government have given the go ahead to begin construction of a new gigantic neutrino detector.

The Japanese cabinet has given the go-ahead for a $600 million giant neutrino detector to be built. Called the Hyper-Kamiokande experiment, it could be a game-changer for the race to detect and study neutrinos

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How are neutrinos observed?

Neutrinos are detected using a specialized apparatus called, funnily-enough, neutrino detectors. These usually consist of a large tank of very pure water that is lined with special detectors.

The idea is to detect the presence of something called Cherenkov light. 

"Cherenkov light is emitted by the neutrinos as they pass through the water at near the speed of light. Therefore the detector detects the effect of the neutrinos interacting with the water and not the neutrinos themselves." - astro.wisc.edu.

Why is neutrino detection so difficult?

Neutrinos are so hard to detect mainly because they are so very small. This makes it almost impossible to detect directly.

For this reason, other means of indirect detection are required to attempt to "observe" them experimentally. 

"Neutrinos are hard to detect because they are 100,000s of times smaller than an electron, so are too small to detect with current equipment. They also don't have a charge and do not interact with any other atomic particles, so it means that it is harder to find when looking at Feynman diagrams." - My Tutor

What is the Hyper-Kamiokande experiment?

The Hyper-Kamiokande experiment is set to be the largest neutrino detector ever built. Containing around 260,000 tonnes of hyper pure water, the detector will be built inside a gigantic cavern next to Hida City's Kamioka mine.

This new detector, once built, will dwarf its already giant sibling the Super-Kamiokande detector. The team behind the project hope their new gigantic detector will bring some groundbreaking discoveries into these elusive particles. 

Reported in the journal Nature, the detector holds some promise: -

"The enormous size of the Hyper-Kamiokande (Hyper-K) will enable it to detect unprecedented numbers of neutrinos produced by various sources — including cosmic rays, the Sun, supernovae, and beams artificially produced by an existing particle accelerator. In addition to catching neutrinos, it will monitor the water for the possible spontaneous decay of protons in atomic nuclei, which, if observed, would be a revolutionary discovery." - Nature

The project is going to be an enormous undertaking and is expected to cost somewhere in the region of $600 million (64.9 billion Japanese Yen). Further investment will be required to upgrade the PARC accelerator 300 km away in Tokai where the neutrino beam will be produced. 

The Japanese government will fund the lion's share of the project with the remaining quarter being provided by international partners like the UK and Canada. 

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How big will Hyper-K be?

The enormous detector will consist of a drum-shaped tank 71 meters deep and 68 meters wide. This enormous structure will be housed in a manmade cavern that will be built using large amounts of explosives. 

"A hall to house the tank will be dug with explosive charges at a site 8 kilometers from the existing Kamioka facilities, to avoid vibrations disturbing the KAGRA gravitational-wave detector, which is about to start operating. The Kamioka site was chosen decades ago because of the existing mining facilities and the high quality of the rock, as well as the abundant supply of freshwater." - Nature.

Sensitive light detectors will line the inside of the tank. These will capture faint flashes that are emitted when neutrinos collide with water atoms. 

hyper-k neutrino detector is a go
The inside of the MiniBooNE neutrino detector, Source: Fred Ullrich/Wikimedia Commons

Physicists around the world are very excited about the potential of the project. This is because it will be able to study differences in the behavior of neutrinos and their antimatter counterparts antineutrinos.

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But, according to Masayuki Nakahata, a physicist at the University of Tokyo, the biggest discovery that Hyper-K could make is proton decay. 

"Proton decay has never been observed and must, therefore, be exceedingly rare — if it happens at all — meaning that the proton has a very long average lifetime, of more than 1034 years." - Nature.

This would be groundbreaking as the current standard model in particle physics does not allow for proton decay to occur. However, many newer theories that could supersede it and promise to unify the fundamental forces do. 

Hyper-K with its much larger volume of water should provide a greater chance of seeing protons decay - - if the predictions are correct. If this phenomenon is not detected, it could help justify extending the average lifetime of protons significantly.  

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