Imagine trying to find an object 10 billion times smaller than an atom--a fragment of matter so tiny that it cannot be seen, isolated or even directly detected by the most sophisticated machines on Earth.

Physicists have good reason to believe that such an inconceivably minuscule object exists, and they're convinced they can find it despite the fact that the odds are decidedly stacked against them. First of all, the object only existed naturally at the very instant the universe was created. The only way to find it now is to conduct monstrously tedious and expensive experiments whose odds of uncovering it are about a trillion to one.

But it's this sort of confounding challenge that these researchers--known as high-energy physicists--live for. Marshaling the forces of some of the most powerful scientific instruments known to man, they are determined to pluck this primordial speck from the deep, subatomic landscape where it's been hiding since the Big Bang.

Actually, in a sense they don't have much of a choice. These scientists are in hot pursuit of the so-called "top" quark, a theoretical linchpin that helps hold together their fundamental assumptions about what matter is and how it's made.

Since the 1960s, such assumptions have rested on a theoryÑfirst proposed by Cal Tech physicists Murray Gell- Mann and George ZweigÑthat explains how matter and energy fit together at the subatomic level. This Standard Model, as it's called, predicts the existence of six fundamental particles called quarks. All but oneÑdubbed the "top" quarkÑhas since been proven to exist. Without confirmation of the top quark's existence, the Standard Model falls apartÑalong with an abiding faith among physicists that what they've figured out so far is, in fact, the way nature works.

"Because of the symmetry of nature, the top quark has to exist," says Dr. Vasken Hagopian (Ph.D. Penn.), high- energy physicist within FSU's physics department. "If we didn't discover it 100 percent, then it would be a disaster; we would say 'Hey, we don't know what we're doing.'"

Hagopian is among 10 Florida State physicists, including four from the campus' Supercomputer Computations Research Institute (SCRI), and several graduate students who belong to one of two international research teams which have been engaged in a friendly competition to find the elusive particle for more than a decade.

The hunt is based on the grounds of the most powerful particle accelerator in the worldÑthe Fermi National Accelerator Laboratory (Fermilab) at Batavia, Illinois, just outside Chicago. The two competing groups, called CDF and DZero (the FSU physicists work with the DZero group) each contain more than 400 researchers representing about 40 universities and research institutions worldwide.

Fermilab is now the sole contender in the race to catch the top quark. Other labs in Switzerland, Germany, Japan and the U.S. were forced to drop out as the energy levels needed to the detect the top grew ever higher, finally eclipsing their capabilities. Most physicists at Fermilab, however, believe they are closing in on the top, and the race may be over in the next few months.

Readers who follow such scientific quests, however, can be forgiven if they thought the race already was overÑand that the CDF group had won. On April 26th of this year, the CDF group announced at a press conference that they finally had evidence pinning down the top quark's place in the family tree of elementary particles. This evidence consisted of a dozen "candidate events"Ñstrong experimental clues pointing to the real thingÑalthough CDF scientists conceded at the time that half of these could be nothing more than interesting background noise. Although the CDF physicists insisted that their data was not statistically strong, publications all over the world heralded the event as the discovery of nature's last hidden building block.

The announcement surprised many of the DZero physicists. Florida State DZero team member Dr. Harrison Prosper (Ph.D. Manchester, England) felt that the press conference was somewhat premature, given the rather small amount of candidate events the CDF group had collected. "It's not that I have anything against press conferences per se," he said. "It's just that it seems to me that one should go to the world and say something when one has something to say."

The DZero group, which has not been collecting data as long as the CDF team (DZero began the search in 1992), hopes that soon they will have a large enough pool of strong candidate events to announce that they, too have evidence for the top quark.

"In one year's time...we may well have more than four times as much data (than the CDF group now has)," said Prosper. "And I happen to believe that with that much data there's a real possibility of being able to obtain about 10 or so events which are gold-platedÑreally very, very clear. Rather than go off to the press and say 'well, we've sort of discovered the top quark,' we'll be able to say we've discovered it, and that will be much more exciting."

How to Catch a Quark

Not many scientists can say that they conduct their research by obliterating the system they study, but that is exactly how the DZero physicists go about their work. The scientists feed streams of protons and antiprotons (particles just like protons but with opposite charge) into a gigantic underground, stainless-steel ring several miles in circumference. The protons and antiprotons, which travel in opposite directions, are magnetically accelerated around the ring until eventually they reach nearly the speed of light. At this point the whizzing particles are smashed into each other, producing a shower of even smaller particles that fly off in every direction. Somewhere in this particle "debris," physicists hope, is the trace of a top quark.

Like prospectors from the Old West, the physicists sift through the subatomic silt created during a proton-antiproton collision, hoping traces of the top quark will emerge. And, more often than not, what actually turns up is merely fool's gold--events that look like the tracks of the top quark but aren't, or ordinary events that have been known for some time.

Up to a million proton-antiproton collisions can occur each second, but since only a fraction of these will yield unusual particles (perhaps one a second), the all-important collider detector, which lies on the accelerator ring and is where the collisions (called events) take place, is responsible for weeding out the ordinary, uninteresting collisions, and preserving the unusual ones for later analysis. The detectors can't actually see the particles themselves. Rather, they recognize each particle's characteristic electronic "signature"Ñthe energy trail the particle leaves as it spins into oblivion.

The problem is, the top quark doesn't have its own unique signature, because it decays into other particles (such as electrons) roughly one-billion trillionth of a second after it's produced. So physicists must search instead for the signatures of the decay products the top quark leaves behind, sort of like detectives searching through a suspect's garbage for clues.

Unfortunately, one of the possible decay products of the top quark is a particle called a neutrino, and neutrinos (which are thought to have no massÑa measure of weight) are virtually impossible to detect. What's more, there are many processes, called background events, which mimic what physicists believe is the top quark's decay pattern. All the noise, of course, further complicates an already confoundingly complex search.

"The problem is that in these particular experiments there aren't enough constraints," laments Prosper. "There are too many things that we don't measure, which means we don't have full information and therefore it is quite impossible to say categorically that this particular event is due to top quark production. All one can do is calculate probabilities," says Prosper.

In other words, forget the "Eureka!" The discovery of the top quark will be hard won, the result of accumulating evidence bit by fragile bit, proving that the top quark appears statistically more often than one would expect to see it from background events alone.

The upshot of all this is that in two years of collecting data almost continuously, out of the 20 million collision events that have been recorded, the DZero group has found only seven which are likely top quark candidates. And only one of these candidates is considered "gold-plated"Ñmeaning that the only plausible explanation is that the top quark really has been there.

The Work at Hand

Given the paucity of genuine top-quark evidence, physicists' ability to recognize what all possible traces might look like is of the utmost importance. To help them, physicists create mammoth computer programs that can simulate what's going on inside of the 5,000-ton DZero collision detector. As it turns out, much of this simulation is played out on computers at Florida State. Prosper, who is deeply involved with simulation and analysis programs, emphasizes the importance of this work.

"The energy of these particles is not measured with infinite precision...and sometimes the directions are not correctly measured," he said. "So a big bulk of the work, especially the work done here (at FSU) is to try to improve the efficiency with which we can find a particular class of top-quark reactions."

Physicists from SCRI also play a large role in DZero detector simulation and analysis. They have written software for the DZero Collaboration that is now being used by experimenters worldwide. A simulation program called GEANT, which was developed by the CERN laboratory in Switzerland, has been adapted to fit the needs of the DZero group.

"One of the problems that people typically have," says SCRI physicist Dr. Saul Youssef (Ph.D. Carnegie-Mellon), "is that physicists or engineers will design some complicated piece of geometry that they would like to be put in the detector...but there's no way for them to test it in advance. So what we did is write a piece of software that is able to simulate the consequences, and the translation is a general one; so this becomes a piece of software that is useful not just in DZero but is used by people all over the world."

Florida State physicist Dr. Susan Blessing (Ph.D. Indiana) is one of the team members who is responsible for the functioning of the giant DZero detector, which took about 10 years to design, assemble and test. One run of the detector typically lasts close to a year, she said. During a run, the detector operates almost continuously, stopping only occasionally for maintenance. Physicists take turns working three eight-hour shifts a day to monitor the data as it comes in and to make sure nothing goes wrong.

Once the data taken from the detector has been stored onto magnetic tape, the physicists try to reconstruct the events that took place from the digitized signals that were actually recorded. Although their primary goal is to find evidence of the top quark, physicists like Blessing also keep their eyes peeled for any other unusual events, labeled "new phenomena," that might have taken place.

"In physics, most of the interesting stuff are things you never expected," says Hagopian. "We're trying to make sure that even the unexpected is caught."

Life After Top

Since the search for the top quark began over a decade ago, scientists have become awed by what the evidence has revealed about whatÑin theory at leastÑsurely ranks as one of nature's most bizarre creations. Scientists now believe that the top quark's mass is about equal to that of an atom of gold. If so, this would make the top quark by far the heaviest of all fundamental particles.

Some physicists believe that because of its improbably large mass, the top quark must be connected in some way to the mechanism that causes mass. Investigating that mechanism, say high-energy physicists, could open the door to a whole new era of physics. Proof of the top quark's existence, when it comes, will thus be an invitation for physicists to tackle yet another riddle-- the origin of mass itself.

Why We Should Care

While the thought of forging new paths in high-energy physics is pretty heady stuff, physicists remain plagued by an inability to communicate the importance of such basic research to the public. "We're not planning to produce new forms of electricity or solve the ozone-hole problem," says Hagopian.

But some physicists feel that not all of their colleagues are this candid, that they tell the public what they think it wants to hear just to win funding for their research. In fact, some are convinced that it was exactly this sort of over- sell that was the downfall of the Superconducting Super Collider (SSC).

"Many of the arguments that we used for the SSC were very specious," says Prosper. "Arguments like, 'we've got to build the SSC because we'll have wonderful spin-offs, we'll be able to cure cancer'....It's condescending, actually. The fact is, there are many bright people out there who are not scientists, who understand what it's all about, and it's quite right that some of them were very put off by these kinds of arguments."

Instead of looking for practical applications, which usually turn up on their own anyway (the popular computer network World Wide Web, for example, was an offshoot of high-energy research at CERN), Prosper and others feel that investigating fundamental aspects of our universe is a worthy endeavor in its own right. Indeed, this kind of inquiry is hardly newÑthe search for the structure of matter began with the ancient Greeks.

So the discovery of the top quark can be seen as both an end and a beginningÑa link between present and future that will bring closure to one set of theories while opening doors to others.