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Nobel Prize Recognizes Particle Physicists, Notes Key BaBar Finding

Nobel laureates Yoichiro Nambu of the U.S. (left), and Makoto Kobayashi (center) and Toshihide Masukawa of Japan. (Photo from the Nobel Foundation.)

The 2008 Nobel Prize in Physics has been awarded to Yoichiro Nambu "for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics," and to Makoto Kobayashi and Toshihide Maskawa "for the discovery of the origin of the broken symmetry which predicts the existence of at least three families of quarks in nature."

The Nobel Foundation's press release includes explicit mention of SLAC's BaBar experiment because it helped confirm one of the key predictions by Kobayashi and Maskawa.

BaBar has studied in detail the phenomenon of CP violation, which is partly responsible for the imbalance between matter and antimatter observed in the universe. CP violation had been observed in particles called kaons or K mesons in 1964. However, it wasn't until Kobayashi and Maskawa developed their theoretical approach in 1972 that the phenomenon could be explained. However, Kobayashi and Maskawa's approach required a third generation of quarks. Experiments conducted soon after this prediction found evidence of the third generation. (The first generation includes the up and down quarks, the second has the strange and charm, and the third consists of the top and bottom.)

The two physicists also realized that studies of B mesons (particles containing bottom quarks) would be ideal for understanding more details of CP symmetry breaking. That concept ultimately led to the creation of the B factories: BaBar at SLAC and Belle at KEK in Japan.

The formulation of Kobayashi and Maskawa's theory, building on earlier work by Nicola Cabibbo, is encapsulated in a mathematical representation called the CKM matrix (employing the trio's initials). The CKM matrix is very well known to BaBar physicists, as many of their experiments directly try to measure numerical elements of that CKM matrix.

The third recipient of the prize, Nambu, was the first to adopt symmetry breaking principles to particle physics. The basic ideas were well known to condensed matter physicists, especially in areas such as superconductivity. It was these general principles that Kobayashi and Maskawa built on and applied to the weak force and which led to their ground-breaking work.

óDavid Harris
SLAC Today, October 7, 2008

More reading:
Nobel Prize press release
Nobel Foundation information for the public
CKM matrix in symmetry magazine
BaBar's window on the weak force in symmetry magazine