How Many Scientists Does It Take To Screw In A Quark?

ALEXANDER WOLSZCZAN IS ONE OF those rare scientists who can explain at cocktail parties what they for a living without making their listeners head for the clam dip. Wolszczan is an astronomer; he searches for planets outside our solar system. But recently someone asked him where in the sky his suspected planets were-in Orion? the Big Dipper? the Pleiades? "I was pinned to the wall," recalls the Pennsylvania State University researcher, who would no sooner wield a telescope to seek out planets than he would consult an astrologer. "I had no idea in what constellation they were. That's how far away from an ordinary person's view of nature we scientists have gotten."

If science has become remote from everyday experience, it has also broken from conventional notions of discovery. In virtually every cutting-edge field, from astrophysics to molecular genetics, the object of discovery is often completely inaccessible to the senses, and the process of discovery has become inferential rather than direct. When Wolszczan "discovered" the first planets outside our own solar system (NEWSWEEK, May 2), he did not spy them through a telescope: he inferred their presence by the pattern of radio beeps coming from the pulsar they orbit. When chemists "discovered" a substance in broccoli that may prevent cancer (NEWSWEEK, April 25), they did not peer at the stalks through a microscope: they looked for the chemical's footprints in the squiggly printout of a chromatograph. Yes, in paleontology one can still stub a toe and, by God, definitely and directly discover a fossil. But in other fields, "no one looks at the thing itself anymore," says physicist Nick Samios, director of Brookhaven National Laboratory in New York. "We look at what the thing does, at the traces it leaves behind."

Or sometimes, traces of traces. Last week physicists announced the first experimental evidence ever for the existence of a long-sought elementary particle called the top quark. In doing so, they completed a 2,000-year-old search for the fundamental, indivisible bits of which all matter, from stars to slugs, is made. Top, as physicists call it, is the last of the suspected building blocks of matter, and finding it provides "a sense of completion," says cosmologist David Schramm of the University of Chicago. It took 440 physicists from 34 countries, working at the Tevatron accelerator at Fermi National Laboratory, 17 years to do it. Top was formed when the Tevatron smashed protons (part of ordinary atomic nuclei) into antiprotons (identical except for a negative electric charge). The burst of energy was converted, as Einstein's E=mc[squared] predicts, into mass-new and much heavier particles. It was like throwing one ping-pong ball at another and creating a bowling ball. One of the bowling balls was top. But no one actually saw top. Nor did instruments sense it, or even detect its tracks. Top lasts for a hundred billionth of a trillionth of a second. Then it falls apart into lighter particles. "We never see it," says Paul Tipton of the University of Rochester. "Just its decay products." Or sometimes the decay products of its decay products.

Physicists will never snare top itself "All of us have thought about it, whether the things we look for are artifacts of our experiment or real," says Nobel laureate Burton Richter, director of the Stanford Linear Accelerator Center (SLAC). It doesn't help that top is so evanescent, completely absent from ordinary matter, and that it last existed naturally during the big bang that created the universe-roughly 15 billion years ago. "How long does something have to exist to be called real?" asks Richter. Such are the fruits of collisions between physics and epistemology.

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The sense of unreality in this quark bunt comes not only from the prey's habit of vanishing instantly, but also from the statistical nature of the discovery. Something other than top could leave the same decay particles that constitute top's signature. The Fermilab physicists calculate that there were five such deceptions possible in the 16 million collisions the computers analyzed. Since the team had 12 signatures of top, they figured some of them had to have been the real McCoy. But there was no one event they could point to and say, There, that's it, that was top. "No single event is convincing," says SLAC's Michael Riordan. "There is not one where you say, 'This could not have been anything other than top'." There was, in other words, no eureka moment. Which of the 12 are real, and which frauds, will never be known. "It's sure not a discovery in the old style, one that hits you between the eyes," says Brookhaven's Mel Schwartz, who shared the 1988 Nobel Prize in physics.

If there is a certain unreality in seeking Cheshire-cat particles that don't even leave behind an honest smile, it is one that scientists mostly sublimate. "To many of us, tweaking the keyboard on a computer [controlling an accelerator experiment] to reconstruct the collisions is reality," says Jay Hauser of the University of California, Los Angeles, a member of the top posse. (But he has a keen appreciation for the difference between his reality and others: his wife is a surgical nurse.)

In fact, the distance between scientists and their target is not new: astronomers in the last century despaired of learning the composition of stars, but then figured out that the light stars send to earth can be broken up by fancy prisms into colors that reveal their chemical ingredients. Rochester's Tipton muses that this disconnect between the subatomic world and the world of humans "is even good for the soul. It shows us that our day-to-day perceptions do not apply to every facet of existence. " But then, Tipton is used to the idea of reality as a moving target: his wife is a minister.

The Fermilab team will keep smashing protons and antiprotons for two more years, hoping for another 100 top events to add to the current 12. A parallel team of 400 scientists, using a different detector in the Tevatron, is continuing its own search. Further collisions should confirm the existence of the last quark, as well as pinpoint its incredible mass-as much as an entire gold atom. Why top is so much heavier than every other basic particle is a mystery whose solution might explain what may be the most fundamental questions of all: Where did mass came from? Why is there this stuff called matter? That understanding, says Fermilab theorist Chris Hill, "would rank on a par with any of the great scientific achievements. This is not the end of the process but the beginning of a new science." If he is right, top will have more than earned its nickname: truth.

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PHOTO: Teamwork: Some of the Fermi 440 who found the missing particle

Physicists have the first evidence of the top quark, one of six quarks with fanciful names. It is the last of the fundamental particles that make up all matter.

How Many Scientists Does It Take To Screw In A Quark? | News