Pushing quarks to the limit.

So far, physicists have experimentally identified five types of quarks: up, down, strange, charm, and bottom. And they expect to find a sixth, called the top quark. But are there any additional quarks? New calculations by a team of physicists at the University of Tsukuba in Japan provide a glimpse of what would happen to interactions between quarks if their number were larger than six. The results suggest that the strong force responsible for keeping quarks under wraps would no longer confine them, meaning that one would be able to detect single, isolated quarks. This finding contradicts accumulated experimental evidence that quarks can't be found in isolation. Y Iwasaki and colleagues report their results in the July 6 PHYSICAL REVIEW LETTERS.

In the June 8 issue, a large group of physicists working with data from the Collider Detector at Fermilab in Batavia, Ill., reported success in detecting significant numbers of B-particles, which result from the production and fragmentation of bottom quarks in high-energy collisions between protons and their oppositely charged counterparts, antiprotons. Because such collisions typically create a tremendous amount of subatomic debris, physicists weren't sure they could sift out B-particles from among the fragments. With this new source of B-particles, researchers may yet find an explanation for the universe's apparent imbalance between matter and antimatter.