About ICRR
From the Director

Takaaki Kajita


The history of the Institute for Cosmic Ray Research (ICRR) began with a cosmic-ray observation hut called Asahi Hut in Mt. Norikura at the altitude of 2,770m. This small hut, built in 1950 with the Asahi Bounty for Science, developed into the Cosmic Ray Observatory (commonly called Norikura Observatory) of the University of Tokyo in 1953. It was the first inter-university research facility in Japan. The Cosmic Ray Observatory was then reorganized to become the Institute for Cosmic Ray Research (ICRR) of the University of Tokyo in 1976. Since then, ICRR has carried out various research activities on cosmic rays as an inter-university research institute.

The headquarters of ICRR is located on Kashiwa-campus of the University of Tokyo in Chiba, Japan. High-energy phenomena in the Universe and elementary particles are studied by observing various cosmic ray particles. Examples of the well-known achievements of ICRR are the observation of a neutrino burst by supernova SN1987A, and the discovery of neutrino oscillations using neutrinos produced by cosmic ray interactions in the atmosphere. ICRR’s three research divisions, Neutrino and Astroparticle division, High Energy Cosmic Ray division, and Astrophysics and Gravity division, effectively promote these scientific activities. ICRR has 4 observatories in Japan; Kamioka Observatory (Kamioka underground, Gifu prefecture), KAGRA Observatory (Kamioka underground, Gifu prefecture), Norikura Observatory (2,770 meters alt., Mt. Norikura, Gifu prefecture), and Akeno Observatory (Yamanashi prefecture). In addition, there are 4 observation bases outside Japan, located in Utah, USA, Yangbajing in Tibet, China, La-Palma, Spain, and Chacaltaya, Bolivia.

In 2010, the Japanese government introduced a new system called “Joint Research/Usage Center” replacing the previous “Inter-University Research Institution” system. ICRR, selected as one of the Joint Research/Usage Centers, continues to collaborate with researchers in the field of cosmic rays and astroparticle physics in Japan and abroad, as with the previous system. ICRR carries out many inter-university research programs: each year, over 100 inter-university research programs are carried out at ICRR. It is notable that most of the scientific outcomes from this institute are the results of the collaborative efforts by many institutions. In order to produce outstanding results, it is imperative that experiments be carried out by international collaborations composed of top-level researchers from all over the world. Hence, most of the experimental collaborations that ICRR is involved in are international ones.

In recent years, many exciting results have been obtained in the field of cosmic ray physics by various observations in the world. ICRR intends to continue to be one of the leading institutions that contribute to the world community of cosmic ray and astroparticle physics. In order to help make decisions for the future research projects at ICRR, ICRR has periodically formed committees whose aim is to recommend our future projects. In particular, since mid. 1990s ICRR’s top priority has been the construction of a gravitational wave detector (KAGRA) to detect gravitational waves which will open up the new field of the gravitational wave astronomy. In 2010, this project was approved and funded by the Japanese government. We thank all of you who have supported this project. In order to manage the project, ICRR has established “KAGRA Observatory” in Kamioka. The construction of KAGRA is carried out with the initiative of this office collaborating with co-host institutions, KEK and NAOJ, and with the collaborators in Japan and abroad. In February 2016, the first observation of the gravitational wave signal was reported by LIGO. The news suggests that the new scientific field called “gravitational wave astronomy” is about to open. KAGRA plans to join the global network of gravitational wave detectors to promote the gravitational wave astronomy together with the other gravitational wave projects. The onsite construction of the KAGRA interferometer is in progress. The initial operation of the KAGRA interferometer with cryogenic mirrors will be carried out in this spring. In early 2019, we expect the completion of the construction of KAGRA, and hope to begin the initial observation run by the end of 2019.

Following the start of the KAGRA construction, we think that it is the time to begin discussing the future research projects of ICRR. For this purpose, we formed the Committee on Future Projects of ICRR at the end of 2011. This committee’s activity concluded with a report issued in September 2013, which recommended several proposals, including CTA, a very high-energy gamma ray observatory, as high-priority future projects of ICRR. In addition, the scientific activities in the past 6 years were reviewed in FY2012 by the External Review Committee. These reports are available on ICRR web. These reports provided ICRR with useful information to move forward to new scientific activities including CTA. In FY 2016, a part of the Japanese contribution for CTA, namely Large Size Telescopes (LST) for CTA-north, has been approved, and the preparation and construction works are in progress. The first LST will begin the observation in the fall of 2017.

It is also important to plan the future of the neutrino research that has been carried out with the Super-Kamiokande detector. Therefore, ICRR has formed the Committee on Future Projects of ICRR in 2016. This Committee has provided the report, concluding that important sciences, such as neutrino physics and proton decay, should be carried out with the next generation water Cherenkov detector (Hyper-Kamiokande), which is about an order of magnitude larger than Super-Kamiokande. In order to realize Hyper-Kamiokande, ICRR together with Kavli-IPMU and the school of Science of the University of Tokyo have created a new organization, called “Next-Generation Neutrino Science Organization”. We are going to do our best to realize Hyper-Kamiokande.

Finally, we sincerely appreciate the strong support of our colleagues in this research field, The University of Tokyo and the Japanese Ministry of Education, Culture, Sports, Science and Technology. They are indispensable for the continuing development and exciting scientific outcomes at ICRR.