Japan has given the green light to the construction of Hyper-Kamiokande (HK or Hyper-K), the world’s largest neutrino detector, which will attempt to elucidate some of the great mysteries of the universe. Among its most ambitious objectives, discover the reason why the matter won the antimatter after the Big Bang allowing our existence. And another perhaps even more amazing: the decomposition of the proton proposed by the Great Unification theory. It is an extremely rare phenomenon that has never been observed and that, if it happens, would put upside down what we think we know about the laws of physics.
Hyper-K will be built inside a gigantic cavern next to the Kamioka mine in the city of Hida, some works that will cost about 600 million euros. The budget for the first year includes 30 million and operations will begin in 2027. The detector will contain 260,000 tons of ultrapure water, more than five times the amount housed by its predecessor, the Super-Kamiokande. Japan will provide approximately 75% of the total project funds and the rest will be covered by its international partners. Spain is studying becoming one of them. Just a few days ago, the project leader, Takaaki Kajita, a physicist from the University of Tokyo and Nobel Prize in Physics 2015 for his co-discovery of the neutrino oscillations, met with the Minister of Science, Pedro Duque, to arrive to agreements about it.
The new Japanese detector “has an unbeatable and unquestionable scientific interest,” says Luis Labarga, head of a group in the Department of Theoretical Physics at the Autonomous University of Madrid dedicated to the development of Hyper-K photodetection units. He is the scientific coordinator of the Spanish participation in the project, in which the Canfranc Underground Laboratory (LSC) has also been involved, where several experiments on neutrinos are carried out. «Spain should be one of the partners of the detector. It would be a serious mistake to stay out, ”says the researcher.
The detector will consist of a drum-shaped tank 71 meters deep and 68 meters wide, “in which the cathedral of Notre Dame de Paris would fit,” Labarga illustrates. The water tank will be coated with the newly developed high sensitivity detectors that will capture the weak flashes emitted by the high-energy charged particles created when a neutrino collides with an atom in the water, causing a charged particle to fire at high speed.
The mystery of asymmetry
The enormous size of Hyper-K will allow it to detect an unprecedented number of neutrinos, phantom particles that barely interact with matter, produced by various sources, including cosmic rays, the Sun, supernovae and also a particle accelerator that He produces them artificially. One of the most interesting aspects is that you can study the differences in the behaviors of neutrinos and their antimatter counterparts, antineutrinos. This asymmetry could help explain how we end up in a universe full of matter and seemingly without a trace of antimatter, one of the greatest mysteries that physics faces. There would be no atoms, no stars. “It would be a fundamental, revolutionary scientific knowledge,” says Labarga. It is logical, since that victory allows us to exist. If he had won the antimatter, there would be nothing but energy and light.
Super-K has already seen evidence of this discrepancy, but both Hyper-K and another major detector in the US called Deep Underground Neutrino Experiment (DUNE), which will also start at the end of this decade, they should be able to measure it with high precision: the Japanese with water and DUNE with liquid argon.
The end of the universe
In addition to trapping neutrinos, the detector will control the water in search of possible spontaneous decomposition of protons in the atomic nuclei, which, if observed, would also be a revolutionary discovery. The stability of matter, of the proton, has been admitted without reservation by most of the scientific community. In fact, according to the current standard model of particle physics, it never disintegrates. However, since the late 70s, new ideas and theories try to replace the existing one and get a unified theory of all the fundamental forces of nature. According to these ideas, the proton (which in reality is not a fundamental particle, but is composed of quarks) would not be stable, but would have an extraordinarily long half-life, over 10 years to 34 years, several orders of magnitude above the current life of the Universe. Disintegration, then, would be an extremely rare phenomenon, if it happens.
“We think it should happen and that’s why we make increasingly large detectors,” Labarga explains. Indeed, because Hyper-K will control a much larger volume of water than Super-K, it will have a better chance of seeing proton decay. If you do not detect the phenomenon, the proton half-life limit will increase tenfold. “It is a fundamental scientific problem with an indestructible theoretical solidity,” says the scientist. Hyper-K “is worth it only for the decay of the proton,” he concludes, while ensuring that this discovery would even have “philosophical and theological implications, since it tells us about the end of the universe.” .