Skip to main content
Personalities

Personalities

Japanese Nobel-prize-winning particle physicist Toshihide Maskawa dies aged 81

30 Jul 2021 Michael Banks
Toshihide Maskawa
Particle pioneer: Toshihide Maskawa did his ground breaking work on the mechanism of 'broken symmetry' in particle physics in the early 1970s (Courtesy: Prolineserver/GFDL 1.2)

The Japanese Nobel-prize-winning physicist Toshihide Maskawa died on 23 July at the age of 81. Maskawa shared half the 2008 Nobel prize with the Japanese physicist Makoto Kobayashi for their work on the mechanism of “broken symmetry” that led to the prediction of a new family of quarks. The other half was awarded to the Japanese–American particle physicist Yoichiro Nambu for applying spontaneous symmetry breaking to particle physics.

Born in in Nagoya, Japan, Maskawa studied physics at Nagoya University and earned a PhD in particle physics from the university in 1967. In 1970 he then moved to Kyoto Univeristy before heading to Kyoto Sangyo Univeristy from 2003 to 2009. From 2010, Maskawa became the first director of the Kobayashi-Maskawa Institute for the Origin of Particles and the Universe at Nagoya University, a position he held until 2018.

Broken symmetries

Symmetry breaking seeks to explain the subtle differences in physics that enables matter to tip the balance with antimatter in the universe. Charge (C) symmetry involves particles behaving like their oppositely charged antiparticles, while “parity” (P) symmetry means events should be the same when the three spatial co-ordinates xand are flipped.

Physicists were sure that all these symmetries held for elementary particles but in the 1950s, physicists discovered that charge symmetry breaks in the weak interaction, which governs radioactive beta decay. In 1956 the theorists Tsung Dao Lee and Chen Ning Yang suggested that P symmetry might break in the weak interaction, which governs radioactive beta decay. Soon after, a famous experiment by Chien-Shiung Wu and colleagues at Columbia University showed that, during beta decay, cobalt atoms emit electrons in a preferential direction. The result validated Lee and Yang’s beliefs and bagged them a Nobel in 1957.

Despite the proof that symmetries could at least be broken individually, most assumed that combined parity and charge symmetry, or so-called CP symmetry, would hold. But in 1964 tests on the radioactive decay of particles known as kaons showed that even CP symmetry could break, a result that won physicists James Cronin and Val Fitch the Nobel prize in 1980. It is the theory that explains this broken symmetry that has handed the 2008 prize to Maskawa.

In 1972, using calculations based on quantum mechanics, Maskawa and Kobayashi formulated the 3 × 3 matrix that describes how the strange quark and down quark inside a kaon can switch to and fro into their antiparticles and, in doing so, occasionally break CP symmetry. Moreover, the mixing in the matrix implied the existence of new quarks – the charm, bottom and top – all of which were discovered over the following decades. The matrix became known as the “CKM” matrix (the “C” being named after the Italian physicist Nicola Cabibbo who proposed the concept of “quark mixing”).

In 2008 Maskawa and Kobayashi shared half of the Nobel prize “for the discovery of the origin of the broken symmetry which predicts the existence of at least three families of quarks in nature.” The other half was awarded to Nambu from the University of Chicago, “for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics”.

Maskawa was not widely known outside of Japan, and much of his work is in his native language. Indeed, it is thought that he had never travelled abroad and only got a passport in order to attend the Nobel prize ceremony in Stockholm in 2008. Yet according to Tim Gershon of the University of Warwick in the UK, Maskawa had an “enormous influence” in his home country. “This helped to make Japan the powerhouse of fundamental science that it is today,” adds Gershon. “Maskawa leaves an important legacy.”

Copyright © 2024 by IOP Publishing Ltd and individual contributors