11

Japan Academy Prize to:

Fumihiko TAKASAKI Professor Emeritus, High Energy Accelerator Research Organization

for “Studies of CP Violation in the B-Meson System”

Outline of the work:

Dr. Fumihiko Takasaki, leading an international research group, discovered CP violation in the B-meson system and clarified the mechanism of CP violation using the B-factory accelerator at the High Energy Accelerator Research Organization (KEK). According to relativistic quantum field theory, every particle has a corresponding antiparticle with the same mass and opposite electric charge. It had long been believed that natural laws are essentially the same for particles and antiparticles. This symmetry between particles and antiparticles is known as CP symmetry. However, in 1964, it was found that CP symmetry is slightly violated in the K-meson decay. Theoretical understanding of CP violation developed with a focus upon the six-quark model proposed by Dr. Makoto Kobayashi and Dr. . However, experimental information concerning CP violation had been limited to the K-meson system for many years, until the B-factory accelerators were built at KEK and the Stanford Linear Accelerator Center (SLAC). B-factories are electron-positron colliding accelerators designed to produce a large number of B-mesons. The difference between the properties of produced B-mesons and their antiparticles is a signal of CP violation. If the six-quark model is correct, CP violation is expected to be significant in B-meson systems. Observation of CP violation requires a large-scale detector equipped with sophisticated technology. In particular, the decay positions of B-mesons should be measured to accuracy of the order of 10 micrometers. KEK and SLAC launched this project in 1990s. From the planning stage, Dr. Takasaki was a central figure in the B-factory project at KEK. He proposed building a B-factory accelerator and organized an international experimental team, Belle, which comprised more than 400 researchers from 15 countries and regions. In the course of its experiments, the Belle group overcame many difficulties through his leadership and insight. Without his extensive knowledge and experience, the project would not have succeeded. Ultimately, both groups at KEK and SLAC achieved the prime objective of verifying the mechanism proposed by Dr. Kobayashi and Dr. Maskawa. This greatly contributed in establishing the Standard Model of elementary particle physics. CP violation is also related to the fundamental question why this universe is made primarily of matter, instead of antimatter. The achievements by KEK and SLAC will provide an important cornerstone for resolving this problem. Besides the B-factory project, Dr. Takasaki has been engaged in many experiments, mostly at KEK. He led the VENUS group in experiments using the TRISTAN accelerator, which was the highest-energy electron- positron collider at the time. The results from the experiments at TRISTAN contributed to the verification of asymptotic freedom in the strong interaction. He also served as the director of the Institute of Particle and Nuclear Studies, KEK from 2006 to 2009. 12

The success of the B-factory project is a monumental event in the history of high-energy physics in . Dr. Takasaki’s contribution to this achievement is widely recognized. He has been a recipient of the Nishina Memorial Prize (2001), the Shuji Orito Prize (2010), and the Panofsky Prize (2016).

List of Main Publications

K. Nakajima, N. Kim, S. Kobayashi, A. Masaike, A. Murakami, A. de Lesquen, K. Ogawa, M. Sakuda, F. Takasaki and Y. Watase, Phase Shift Analysis of the Reaction K+N → KN below 1.6 GeV/c, Phys. Lett. B 112, 80-82 (1982) K. Ogawa, K. Hayashi, M. Iwai, T. Sumiyoshi, F. Takasaki, Y. Teramoto, T. Uehara, S. Sugimoto, H. Kusumoto and H. Yoshida, The VENUS Barrel Electromagnetic Calorimeter, Nucl. Instrum. Meth. A 243, 58-66 (1986) H. Yoshida et al. (VENUS Collaboration), Measurement of R and Search for New Heavy Quarks in e+e- Annihilation at 50 and 52 GeV Centre-of-mass Energies, Phys. Lett. B 198, 570-576 (1987)

K. Abe et al. (VENUS Collaboration), Determination of the QCD Scale Parameter ΛMS with QCD Cascade on the Basis of the Next-to-leading Logarithmic Approximation, Phys. Lett. B 240, 232-236 (1990) Y. Funakoshi et al., Asymmetric B-factory Project at KEK, AIP Conf. Proc. 214, 575-591 (1990)

K. Abe et al. (Belle Collaboration), A Measurement of the Branching Fraction for the Inclusive B → Xsγ Decays with the Belle Detector, Phys. Lett. B 511, 151-158 (2001) K. Abe et al. (Belle Collaboration), Observation of Large CP Violation in the Neutral B Meson System, Phys. Rev. Lett. 87, 091802 (2001) K. Abe et al. (Belle Collaboration), Observation of Double cc - Production in e+e- Annihilation at √s ≈ 10.6 GeV, Phys. Rev. Lett. 89, 142001 (2002) K. Abe et al. (Belle Collaboration), Improved Measurement of Mixing-induced CP Violation in the Neutral B Meson System, Phys. Rev. D 66, 071102(R) (2002) S.-K. Choi et al. (Belle Collaboration), Observation of a Narrow Charmoniumlike State in Exclusive B± → K± π+π-J/ψ Decays, Phys. Rev. Lett. 91, 262001 (2003)

P. Krokovny et al. (Belle Collaboration), Observation of the DsJ (2317) and DsJ (2457) in B Decays, Phys. Rev. Lett. 91, 262002 (2003) K. Abe et al. (Belle Collaboration), Study of B - → D**0π -(D**0 → D(*)+π -) Decays, Phys. Rev. D 69, 112002 (2004) P. Koppenburg et al. (Belle Collaboration), Inclusive Measurement of the Photon Energy Spectrum in b → sγ Decays, Phys. Rev. Lett. 93, 061803 (2004) S.-K. Choi et al. (Belle Collaboration), Observation of a Near-Threshold ωJ/ψ Mass Enhancement in Exclusive B → KωJ/ψ Decays, Phys. Rev. Lett. 94, 182002 (2005) K. Abe et al. (Belle Collaboration), Observation of a Charmoniumlike State Produced in Association with a - J/ψ in e+e Annihilation at √s ≈ 10.6 GeV, Phys. Rev. Lett. 98, 082001 (2007)