MAKING SENSE OF A WEIRD NEW WORLD

THERE'S nothing space-age about Drasko Jovanovic's laboratory. A makeshift clutch of portable buildings on a wind-swept prairie, it looks like something left over from a down-at-heel school district. On the coldest winter days, coffee spilled on the linoleum floor freezes solid. Even the video screens ranked along the walls of his homemade control room are a mismatch of styles, shapes, and sizes. But there's nothing down-home about the experiments this mustachioed Yugoslav conducts here. As he sits at a computer keyboard, his face aglow in the light from several screens, the enthusiasm is almost palpable. Once again, he's on the trail of the neutrino. What troubles Dr. Jovanovic is not that these subatomic bits of matter have no electric charge: That's what their Italian name (``the little neutral ones'') means. Nor is he particularly bothered by the fact that they have no size - that they are, in physicists' language, ``pointlike,'' lacking all dimension. He even accepts the fact that neutrinos, naturally produced by nuclear reactions on the sun, rain down onto the earth in massive amounts - and pass harmlessly right through plants, animals, people, and the entire globe, emerging untouched out the other side.

Instead, what really bothers him is his conviction that these particles - for particles they surely are - have no mass at all.

``How can it be massless,'' he muses, ``and yet have these properties?''

The ``properties'' they do have, - such as ``left-handed spin'' and a velocity equal to the speed of light - show up in the vast, elaborate experiment Jovanovic has set up here at the Fermi National Accelerator Laboratory. Whenever his experiment is running, the world's largest atom smasher (or ``particle accelerator,'' as it is properly known) blasts a five-foot-wide beam of neutrinos down an earth-covered tunnel toward his buildings.

The beam arrives in bursts, 10 billion particles every couple of seconds. He targets the bursts onto 60,000 tons of high-grade steel plates - left over, he says, from American military shipbuilding operations during World War II. Between them is sandwiched layer upon layer of sensitive detectors. The neutrinos glide harmlessly through the steel and the detectors - and through the back wall of the laboratory as well. And then, Jovanovic says with a chuckle, his arm extended eastward, they just keep going - ``through the bedrooms of West Chicago and out across Lake Michigan,'' before they vanish on their trajectory into space.

But now and then, deep within the vast, empty spaces that make up the molecules of the steel plates, something happens. A lone neutrino collides head-on with a quark - a fundamental particle inside a proton at the center of an atom. The smashup produces a bevy of new particles. And some of these leave their mark for the human world to trace - like the long-tailed muon he suddenly exclaims over, stabbing his finger at the telltale green track arcing across his computer screen. It's as close as you can come, Jovanovic explains, to ``seeing'' a subatomic particle.

Baryons, mesons, and other odd stuff

Just what are these particles? For thousands of physicists around the world, answering such questions is a life's work. On the one hand, the answer is simple. Neutrinos, along with electrons, belong to a family of elementary particles called leptons - which, along with baryons, mesons, and other oddly named bits of stuff, are thought to be the fundamental constituents of matter. They are what lies at the end of a centuries-long search for the basic, indivisible building blocks of the universe - for the ``solid, massy, hard, impenetrable, movable Particles'' that Sir Isaac Newton thought made up all matter.

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