World Class Researchers

Toshihide Maskawa

Dr. Toshihide Maskawa


Born in Nagoya City


Graduated from Nagoya City Kouyou High School


Ph.D., Graduate School of Science, Nagoya University (Doctor of Science)


Research Associate, School of Science, Kyoto University


Professor, Yukawa Institute for Theoretical Physics, Kyoto University


Councilor, Kyoto University


Professor, Yukawa Institute for Theoretical Physics, Kyoto University


Retirement (Professor Emeritus, Kyoto University)


Distinguished Professor, Nagoya University 


Director, Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University


The Attentive Dr. Sakata

Dr. Sakata was not only a person with the conviction to do independent elementary particle theory research but was also attentive in teaching. Dr. Sakata's way of teaching was to maximize the autonomy of the students, so that students could reach their full potential. The following incident once occurred.

When Mr. Maskawa was a graduate student, there were many unpaved roads near Nagoya University, and his shoes were often covered with mud. One day, after it had rained, Mr. Maskawa left after a discussion in Dr. Sakata's room. After a while, Mr. Maskawa knocked on the door of Dr. Sakata's room to continue the discussion, and ended up opening the door before he received a response. He found Dr. Sakata carefully cleaning the floor with a mop, where it had gotten dirty from the mud.

Apparently Dr. Sakata considered that if he told students to scrape the mud off their shoes before entering his room, they would feel uncomfortable or afraid to talk to him and might stop coming.


Let's Wrestle, Maskawa!

The atmosphere in the Department of Physics is well captured in this photograph. Professor Satio Hayakawa, who was already a world leader in space physics (X-ray astronomy), wrestled with Mr. Maskawa, who was a graduate student at the time. Mr. Maskawa must have put in a good effort, as there is a picture of Professor Hayakawa holding Mr. Maskawa up on his shoulders. The picture shows the non-restrictive atmosphere that existed in the Physics Department at the time.


Broken Charge Parity (CP) Symmetry and the Kobayashi-Maskawa Matrix

In 1972, at the time the Kobayashi-Maskawa paper was written, many researchers doubted the very existence of the quark. Researchers who believed that the quark existed hypothesized that only 3 types of quark (u, d, s) existed, and only a handful of cutting-edge researchers had begun to investigate the existence of the 4th type, the charm quark (c). In this situation, Makoto Kobayashi and Toshihide Maskawa investigated the possibility of using quantum mechanics theory, which has a weak interaction that can renormalize the broken CP symmetry, as they already knew from tests. Their results were surprising. Even though they hypothetically recognized the existence of the quark, with the 4-type model (u, d, c, s), they ended up proving that the broken CP symmetry will not occur! With the weak-interaction quantum mechanics, multiple parameters are introduced that state the changes in u↔d. Similarly, parameters that state the changes between u↔s, c↔d, and c↔s were introduced,and these were put together in the form of a matrix. The 4 parameters included in this matrix were insufficient to prove the broken CP symmetry. So how were they to theoretically prove this symmetry? Makoto Kobayashi and Toshihide Maskawa investigated a 6-type model with 6 types of quarks. In this case, the weak-interaction quantum mechanics becomes a theory with 9 parameters, and makes it possible to prove the broken CP symmetry. Using the small experimental clue of the broken CP symmetry and clear theoretical observation, Makoto Kobayashi and Toshihide Maskawa managed to predict the existence of the 5th and 6th quarks, which no one believed were real at the time.


Nine Matrix Parameters in the Kobayashi-Maskawa Theory


Verification of the Kobayashi-Maskawa Theory

Discovery of Six Types of Quarks and Leptons

After particles were discovered in 1974, the concept of the quark was quickly accepted by particle physics researchers.  By thinking about the binding situation of the charm quark and anti-particle, they were able to clearly explain various properties. Two years after the Kobayashi-Maskawa theory, people finally started to believe the 4-quark theory. Then, the 5th lepton (tau (τ) lepton) and the 5th quark (bottom quark) were discovered in 1976 and 1977, and the Kobayashi-Maskawa theory could finally bask in the limelight. However, they had to wait a long time until all the particles (6 types of quarks and leptons) were discovered. The 6th quark (top quark) was discovered in 1995, and the 6th lepton (tau neutrino) was reported discovered in 2000.


CP Breakdown Due to B Meson Decay

Ichiro Sanda (Professor Emeritus at Nagoya University) showed that the Kobayashi-Maskawa theory predicts that the decay of the B meson will cause a major broken CP symmetry. Accurate measurement of the various properties of the B meson makes it possible to identify the various parameters included in the Kobayashi-Maskawa theory. This is a good framework in terms of using tests to verify the Kobayashi-Maskawa theory. Two B factory tests were run for this objective. One test was run at the High-Energy Accelerator Research Organization (KEK) in the city of Tsukuba, Ibaraki Prefecture , and the other test was run at the SLAC National Accelerator Laboratory in the US. The Nagoya University test group participated in the KEK test. The accelerator used in the KEK test has the capability to generate more than 1 million B meson pairs per day, and the decay of the generated B mesons was measured and recorded by the Belle detector. Measurements for the Japanese test started in 1999, competing with the American test, and in 2001 major broken CP symmetry was reported for B mesons. Currently, B factory tests in Japan and the US have measured various amounts of B meson decay, and the Kobayashi-Maskawa theory has been verified with high accuracy.


Belle Detector and KEK B Accelerator used in the verification of the Kobayashi-Maskawa Theory

KEK B accelerator
High-Energy Accelerator Research Organization (KEK) (City of Tsukuba, Ibaraki Prefecture)

Determination of the Kobayashi-Maskawa theory parameters. All the measurement results indicate the same parameters, and support the Kobayashi-Maskawa theory.