Shoichi Sakata

Shoichi Sakata (坂田 昌一) was a Japanese physicist and Marxist who was internationally known for theoretical work on the subatomic particles.

He proposed the two meson theory, the Sakata model (an early precursor to the quark model), and the Pontecorvo–Maki–Nakagawa–Sakata neutrino mixing matrix.

After the end of World War II, he joined other physicists in campaigning for the peaceful uses of nuclear power.

Sakata also became closely acquainted with Katō Tadashi, who would later co-translate Friedrich Engels's 1883 unfinished work Dialectics of Nature into Japanese.

According to Sakata, Dialectics of Nature and Vladimir Lenin's 1909 work Materialism and Empirio-criticism became formative works for his thinking.

Sakata was born in Tokyo, Japan on January 18, 1911, to a family that held a tradition of public service.

He was the eldest of six children of Tatsue Sakata and Mikita Sakata.

At the time of Sakata's birth, Mikita was secretary to Prime Minister Katsura Tarō, who became Sakata's godfather.

While attending Kōnan Middle School in Hyōgo Prefecture in 1924, Sakata was taught by the physicist Bunsaku Arakatsu.

During his time as a student at Kōnan High School from 1926 to 1929, Sakata attended a lecture given by the influential physicist Jun Ishiwara.

Sakata got in to the Kyoto Imperial University in 1930.

When he was a second year student, Yoshio Nishina, a granduncle-in-law of Sakata, gave a lecture on quantum mechanics at the Kyoto Imperial University.

Sakata became acquainted with Hideki Yukawa and Shin'ichirō Tomonaga, the first and the second Japanese Nobel laureates, through the lecture.

After graduating from the university, Sakata worked with Tomonaga and Nishina at Rikagaku Kenkyusho (RIKEN) in 1933 and moved to Osaka Imperial University in 1934 to work with Yukawa.

Yukawa published his first paper on the meson theory in 1935 and Sakata closely collaborated with him for the developments of the meson theory.

Possible existence of the neutral nuclear force carrier particle Pion was postulated by them.

Accompanied by Yukawa, Sakata moved to Kyoto Imperial University as a lecturer in 1939.

Sakata and Inoue proposed their two-meson theory in 1942.

At the time, a charged particle discovered in the hard component cosmic rays was misidentified as the Yukawa's meson (Pion, nuclear force career particle).

The misinterpretation led to puzzles in the discovered cosmic ray particle.

Sakata and Inoue solved these puzzles by identifying the cosmic ray particle as a daughter charged fermion produced in the decay.

A new neutral fermion was also introduced to allow decay into fermions.

We now know that these charged and neutral fermions correspond to the second generation leptons μ and in the modern language.

They then discussed the decay of the Yukawa particle,

Sakata and Inoue predicted correct spin assignment for the muon, and they also introduced the second neutrino.

They treated it as a distinct particle from the beta decay neutrino, and anticipated correctly the three body decay of the muon.

Sakata moved to Nagoya Imperial University as a professor in October 1942 and remained there until his death.

The English printing of Sakata-Inoue's two-meson theory paper was delayed until 1946,

one year before the experimental discovery of π → μν decay.

The name of the university was changed to Nagoya University in October 1947 after the end of the Pacific War (1945).

Sakata reorganized his research group in Nagoya to be administrated under the democracy principle after the War.

Sakata stayed at the Niels Bohr Institute from May to October 1954 at the invitation of N. Bohr and C. Møller.

During his stay, Sakata gave a talk introducing works of young Japanese particle physics researchers, especially emphasizing an empirical relation found by Nakano and Nishijima, which is now known as the Nakano-Nishijima-Gell-Mann (NNG) rule

among the strongly interacting particles (hadrons).

After Sakata returned to Nagoya, Sakata and his Nagoya group started researches trying to uncover the physics behind the NNG rule.

Sakata then proposed his Sakata Model

in 1956, which explains the NNG rule by postulating the fundamental building blocks of all strongly interacting particles are the proton, the neutron and the lambda baryon.

The positively charged pion is made out of a proton and an antineutron, in a manner similar to the Fermi-Yang composite Yukawa meson

model,

while the positively charged kaon is composed of a proton and an anti-lambda, succeeding to explain the NNG rule in the Sakata model.