Frederick II among groups working on Hyper-Kamiokand experiment

The University of Naples Federico II is among the groups participating in the Hyper-Kamiokande (Hyper-K) experiment. Last July 31, in Japan's Gifu prefecture, the excavation of the colossal cavern that will house the experiment's main particle detector (Hyper-K) was completed.

Italy's participation in Hyper-Kamiokande involves, in addition to the Federico II University, INFN's Bari, Naples, Padua, Pisa and Rome sections, the Polytechnic University of Bari, the University of Campania "Luigi Vanvitelli," the University of Salerno, the University of Padua, the University of Pisa and the Sapienza University of Rome.

Coordinating the excavation work is the University of Tokyo, which together with the Japanese research institute KEK, High Energy Accelerator Research Organization, is leading the international scientific collaboration of the Hyper-K project, to which 630 male and female researchers from 22 different countries are contributing, including Italy with the National Institute of Nuclear Physics (INFN). The Hyper-K project, which officially began in February 2020, aims to observe neutrinos from supernovae explosions and test the Grand Unification Theory (GUT) and the history of the evolution of the universe through the study of proton decays and the so-called "CP violation" (the asymmetry between neutrinos and antineutrinos) by analyzing neutrino beams produced by the J-PARC accelerator 300 kilometers away. The heart of the project will be a next-generation particle detector, consisting of a giant tank with a volume more than eight times that of its predecessor, Super-Kamiokande: it will contain 260 thousand cubic meters of ultra-pure water and will be equipped with innovative photosensors, 20 thousand high-sensitivity photomultipliers (PMTs) and 800 multi-PMTs.

The detector is being built 600 meters deep in the giant cavern whose excavation has just been completed under a mountain in the city of Hida. This cavern is one of the largest man-made spaces ever excavated in rock: it consists of a cylindrical section 69 meters in diameter, nearly 73 meters high and topped by a 21-meter-high dome. The challenging excavation work was thus the result of an ambitious engineering feat that required numerous studies and preliminary excavations. Starting in August, work will begin to transform this cavern into the giant Hyper-K reservoir, to be followed in 2026 by the construction of the detector.

Meanwhile, mass production of the new photosensors and other electronic components that will make up the detector is proceeding in Japan, Italy and the other countries in the collaboration. In particular, a new laboratory is being set up at the INFN section in Naples, which is coordinating the contribution of the countries participating in the realization of the multi-PMTs (Canada, Poland, Czech Republic, Mexico and Greece), where more than a third of the multi-PMTs that will be installed in Hyper-K will be assembled. In addition, the photomultiplier digitization electronics are being designed by INFN, which is responsible for the production of 2,000 boards that will be shipped to CERN from mid-2026 to be calibrated and integrated in underwater containers with the rest of the experiment's electronics produced in Korea, France, Japan, Poland, Spain, Switzerland and the United Kingdom. All of the detector components inside the Hyper-K tank are expected to be installed by 2027, after which the tank will be filled with ultra-pure water and the experiment will go into operation in 2028.

In parallel with the work on the construction of Hyper-K's main detector, KEK is leading the upgrade of J-PARC's accelerator neutrino beam and the construction of a new intermediate detector in Tokai Village, Ibaraki Prefecture, located less than a kilometer from the origin of the neutrino beam. In addition, Hyper-K will consist of a third detector, installed only 280 meters away from the J-PARC accelerator, to which INFN has contributed special new particle detectors, known as the "Time Projection Chamber - TPC."