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Neutrinos and Beyond — Opening a New Era of Cosmic-Ray Research

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Neutrinos and Beyond — Opening a New Era of Cosmic-Ray Research ADVERTISEMENT FEATURE THE UNIVERSITY OF TOKYO Neutrinos and beyond — Opening a new era of cosmic-ray research Takaaki Kajita, a recipient of the 2015 that neutrinos are massless. These discov- Nobel Prize in Physics, and other re- eries, which resulted in Kajita’s 2015 Nobel searchers at the University of Tokyo’s Prize in Physics, were made a team led by Institute for Cosmic Ray Research (ICRR) him in 1998. have been exploring new realms in par- Kajita acknowledged his success owed ticle physics research. Kajita’s work on a lot to the strong support he received neutrinos and related research at ICRR from two mentors and former supervisors is leading the world in this field. — Masatoshi Koshiba and Yoji Totsuka. Koshiba was awarded the 2002 Nobel Prize The path to a Nobel prize in Physics for detecting neutrinos pro- Particle physics and astrophysics are duced in supernovae using Kamiokande, among the most active research fields at the predecessor of Super-Kamiokande. the University of Tokyo, and its Institute for Totsuka led the Super-Kamiokande proj- Cosmic Ray Research (ICRR) is leading the ect as Koshiba’s successor. Totsuka’s con- world with explorations in these areas. ICRR tribution was so great that many believe is best known for its research on neutrinos he would have shared the Nobel Prize with using the world’s largest underground neu- Kajita if he were alive. trino detector, Super-Kamiokande. The de- Kajita’s award-winning work dates tector is located in a mine in central Japan back to 1986 when he earned his PhD for and is filled with 50,000 tons of pure water. researching proton decay. Soon after that, Neutrinos, which are electrically neutral Kajita began to upgrade the software he subatomic particles, exist in three different was using to separate the proton-decay sig- forms — electron, muon and tau. They are nal from the background noise produced generated in various places, including the by atmospheric neutrino interactions. He centre of the Sun and the Earth’s atmo- discovered that his data did not match the- sphere. Although neutrinos are the most oretical calculations and began to search abundant particle in space after photons, for the cause of this discrepancy. He was they are hard to observe because they unable to find any problems with the data rarely interact with matter. But they hold analysis or the simulation of atmospheric the key to many questions about how the neutrino interactions. The Kamiokande Universe was formed. collaboration reported this result in 1988, Researchers at ICRR have discovered but the academic community was scepti- many important properties of these enig- cal. “The result disagreed with those ob- matic particles, including the fact that neu- tained by other researchers.” Kajita recalls. trinos oscillate, or change from one type to “But Koshiba and Totsuka understood the another, as they travel through the Earth. importance of the Kamiokande data and One implication of this finding is that neu- gave me constant support.” trinos have mass ― a conclusion that has The breakthrough came in 1996 when forced scientists to reassess the standard Super-Kamiokande began operating; with- Kamioka Observatory, Kamioka ICRR, The University of Tokyo model of particle physics, which predicts in two years Kajita’s team had definitively © Advertiser retains sole responsibility for content UOT.indd 1 2/3/16 7:14 PM ADVERTISEMENT FEATURE proved that neutrinos oscillated. They Gamma rays and gravitational waves the next year. Already, more than 200 re- presented this finding at the International ICRR’s exploration of new research fields searchers from around the world are par- Conference on Neutrino Physics and goes beyond neutrinos. The institute is ticipating in the KAGRA project. Astrophysics. “To my surprise, the audi- participating in the international project to Worldwide collaboration in this area ence welcomed my presentation and gave build the Cherenkov Telescope Array (CTA), is expected to accelerate. ICRR is poised me a standing ovation,” Kajita says. a next-generation observatory of very high- to contribute to this new field of gravita- Neutrinos and beyond energy gamma rays. CTA will detect the tional-wave astronomy by completing the More projects with Super-Kamiokande highest-energy photons ever observed, construction of KAGRA and participating Since then, neutrino research has been which will lead to a deeper the understand- in international observation networks as — Opening a new era steadily advancing. Some 120 research- ing of star formation in the evolution of the soon as possible. Through collaborating ers from seven countries take turns to Universe and many other events that can- with researchers around the world, ICRR analyse the data that is being continually not be observed using current technolo- aims to elucidate the mysteries of the of cosmic-ray research generated by Super-Kamiokande. The fa- gies. In the CTA project, ICRR’s Cherenkov Universe, by, for example, detecting the cility is operated under the supervision Cosmic Gamma Ray Group is developing birth of black holes formed by the merger of Masayuki Nakahata, head of Kamioka large-scale telescopes in collaboration with of binary neutron stars. Observatory and solar neutrino specialist. researchers in Japan, the USA and Europe. Meanwhile, Yoichiro Suzuki, deputy direc- Another important project at ICRR is Promoting cross-border cooperation tor of the Kavli Institute for the Physics the Large-Scale Cryogenic Gravitational All ICRR’s projects are undergirded by the and Mathematics of the Universe (Kavli Wave Telescope (KAGRA). The first-stage efforts of graduate students and young re- IPMU) at the University of Tokyo, greatly facility was completed in October 2015. searchers, who perform vital activities rang- contributed to explaining the discrepancy Gravitational waves are the curvature of ing from the construction of equipment to between data and theory for solar neu- space–time and they propagate at the data analysis. This is true for all the research trinos, which had long puzzled research- speed of light according to Einstein’s done at the University of Tokyo. Young ers. Suzuki and Kajita were awarded the theory of relativity. On 11 February 2016, scientists are essential for research, and 2016 Breakthrough Prize in Fundamental the Laser Interferometer Gravitational- they sometimes create new research fields. Physics for their roles in the discovery and Wave Observatory (LIGO) in the USA and As a world hub for knowledge collabora- study of neutrino oscillation. its international collaborators made the tion, the University of Tokyo is supporting Neutrino research will be further acceler- momentous announcement that they had diverse research activities and developing ated in the next few years with the upgrade detected gravitational waves. “Detection of an environment where young researchers of Super-Kamiokande, which will allow it gravitational waves is very difficult, but the can explore without constraints. To this to detect supernova neutrinos more ef- research — once thought impossible — is end, the university makes proposals to ficiently. There are also plans to build an- moving on thanks to the steady advance of the government as well as reviewing and other detector, Hyper-Kaimokande, whose science and technology and the endeavors reforming internal systems and publicizing volume will be 20 times greater than that of many researchers,” says Shinji Miyoki, as- its research activities. Support for young of Super-Kamiokande. This mega-detector sociate professor of ICRR and a member of scientists, who will play a key role in next- is expected to begin operation in 2025 the KAGRA project. generation research, is vital and should be and the discovery of particle–antiparticle Researchers are now testing the laser made available by both universities and asymmetry in neutrinos is one of the ma- interferometer and plan to commence its governments. As collaborative projects jor goals for it. operation with cryogenic mirrors within between researchers in different countries are becoming more prolific, it is crucial to create an environment in which research- Harvard University ers can flexibly and actively participate Stanford University in global projects, interact with scientists MassachuseHs InsJtute of Technology (MIT) around the world and create new values. University of Tokyo University of Oxford University of Cambridge University of California, Berkeley 0 100 200 300 400 500 600 700 800 900 Contact Nature Index ranking Website: www.u-tokyo.ac.jp/en www.facebook.com/UTokyo.News.en → The publication output of the University of Tokyo is ranked fourth in the world in terms of the weighted fractional count (data period: 1 December www.twitter.com/UTokyo_News_en 2014–30 November 2015). www.youtube.com/user/UtokyoPR Phone: +81-3-3811-3393 Advertiser retains sole responsibility for content UOT.indd 2 2/3/16 7:14 PM.
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