The Institute for Cosmic Ray Research (ICRR) conducts observational studies of cosmic rays from various aspects. Its predecessor was an experimental hut called Asahi Hut, on Mt.Norikura built on an Asahi Academic Grant. In 1953, it developed into the Cosmic Ray Observatory of The University of Tokyo. This observatory was the Japan’s first inter-university research facility.
In 1957, the observatory took a pioneering initiative to internationalize, and participated in worldwide observation experiments of the International Geophysical Year (IGY). In the same year, the observatory started the air shower observation, and in the following year, it started utilizing an emulsion chamber for cosmic ray observations. Since then, the observatory has operated observation experiments steadily with these instruments.
In 1972, the construction of Mutron (electromagnetic spectrometer) was commenced, improving the experimental facilities. In 1973, two international projects of the Japan Society for the Promotion of Science – a deep underground experiment at Kolar Gold Mine in India and a high-altitude experiment on Mt. Chacaltaya in Bolivia- were incorporated into the activities of the observatory. In 1975, the construction of Mutron was completed. In the same year, the construction of Akeno Observatory began.
In 1976, the Cosmic Ray Observatory was reorganized to become the Institute for Cosmic Ray Research (ICRR). ICRR absorbed the 3 sections of the Cosmic Ray Division of the Institute for Nuclear Study of The University of Tokyo, which had conducted similar research since 1956, to become an institute comprising 6 divisions and 1 facility. In 1977, the Akeno Observatory was formally recognized as a second adjunct facility. In 1979, a square kilometer scale air-shower detector array was installed at the Akeno Observatory, and an emulsion chamber on Mt. Fuji. In 1981, Japan-China joint research was initiated using the emulsion chamber. In 1983, a proton decay experiment was started as a joint use experiment in Kamioka, and the construction of facilities for studying primary cosmic rays was completed.
From 1985, ICRR started to produce increasingly significant experimental results, and further improved its experimental equipment. In 1987, the Kamioka Observatory succeeded to detect neutrinos from a supernova for the first time in the world. In the same year, the construction of a 100-square kilometer scale wide-area air-shower detector was commenced at the Akeno Observatory. In 1988, the Kamioka Observatory observed a deficit of solar neutrinos, and in 1989, the Norikura observatory observed a considerable increase in cosmic neutrons in solar flare. In 1990, the construction of the wide-area air-shower detector at the Akeno Observatory was completed. In 1991, the construction of Super-Kamiokande was started. In 1992, the joint use experiment in Australia observed ultra-high-energy gamma rays for the first time in the southern hemisphere. In the same year, a gravitational wave group joined ICRR. In 1993, the construction of the air-shower gamma-ray detector started in Tibet. In 1994, the Akeno Observatory observed a significant shower with its energy beyond the theoretical limit, and the Kamioka Observatory detected an anomaly in atmospheric neutrinos. In 1995, the Kamioka Observatory became the third adjunct facility of ICRR. In 1996, the construction of Super-Kamiokande was completed, and the full-scale observation began. In 1998, the Super-Kamiokande group reported, after two-year observation, that neutrinos have masses.
In 1999, in order to further study the masses of neutrinos, ICRR started a long-baseline neutrino experiment in which the Super-Kamiokande detected the neutrinos artificially produced by an accelerator at the High Energy Accelerator Research Organization. ICRR also established the Research Center for Cosmic Neutrinos in the aim of paving the way for new fields of neutrino research by integrating data and scientific ideas. Further, ICRR was granted a Scientific Research Fund for a COE (Center of Excellence), which helped significantly improve the ultra-high-energy gamma-ray telescopes in Australia.
In 2003, ICRR was granted a Scientific Research Fund to construct the Telescope Array (TA) experiment to investigate the origin of extremely high-energy cosmic rays. After five years of construction, TA started observation in 2008.
On April 1, 2004, The University of Tokyo became an independent administrative entity, and ICRR was recognized to house 3 research divisions. On April 1, 2010, ICRR renewed its inter-university research activities as a new “Joint Usage/Research Center”. In July 2010, the Large Cryogenic Gravitational wave Telescope project named “KAGRA” was approved by the “Leading-edge Research Infrastructure Program” of MEXT. The construction of KAGRA began in the same year. ICRR established the Gravitational Wave Project Office on April 1, 2011, to promote the construction of KAGRA.
In 2010, T2K, or Tokai to Kamioka Long Baseline Neutrino Oscillation Experiment, started its operation, and in June 2011 observed the indication of a new type of neutrino oscillation in which a muon neutrino transform into an electron neutrino. The data from T2K show clear evidence for muon-neutrino to electron neutrino oscillations by 2014.
In March 2012, very high-energy gamma-ray observatory in Australia, the CANGAROO experiment, ended its operation. The gamma-ray studies were taken over by the CTA (Cherenkov Telescope Array) project.
In April 2016, KAGRA was established in Hida city, Gifu prefecture as a base for KAGRA project.
In November 2018, ICRR renewed its inter-university research activities as an “International Joint Usage/Research Center.” In October 2018, the first Large Size Telescope (LST) of CTA project was completed at La Palma in Canary Islands, Spain. High Energy Astrophysics Facility in Canarias was established as a base for the project in April, 2019.
KAGRA, completed in October 2019, started its observation for gravitational waves in February 2020. In February 2020, the budget for the first-year construction of Hyper-Kamiokande was approved by the Japanese Diet, and the construction of Hyper-Kamiokande began.