WHAT'S HIDING IN THE QUARKS?

By MICHAEL D. LEMONICK

PHYSICISTS WERE UNDERSTANDABLY overjoyed in 1994 when they discovered the top quark. At last, after 17 years of searching, they had found the sixth--and, according to the theorists, the last--of matter's tiniest, most fundamental building blocks. The most troublesome loose end in the so-called Standard Model of particle physics had been tidied up.

Or so they thought. According to a report in the current Science, the same people who discovered the top quark may have inadvertently made a much more revolutionary discovery. Contrary to what physicists have believed for the past 30 years, quarks may not be the most basic units of matter after all. Although the results are highly preliminary, the possibility of so startling a conclusion has scientists scrambling for a more conventional explanation for what they're seeing.

The evidence comes from collisions between subatomic protons and antiprotons inside the giant Tevatron accelerator at the Fermi National Accelerator Laboratory near Chicago. The type of particle debris that spews out of such collisions tells scientists what the original particles were made of. That's how quarks were discovered in the first place.

But the Tevatron is so powerful that it can probe the structure within quarks themselves--structure that had, until now, been presumed not to exist. If, as it seems, there really is something lurking inside the quark, the whole Standard Model may have to be trashed. And subatomic physics may suddenly become a lot more interesting than even its practitioners suspected.

--By Michael D. Lemonick