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What the top quark means to me

by Calvin W. Johnson

Call it the Godzilla particle. It's enormously heavy. Last awake in a prehistoric era, it slumbers deep beneath a quantum sea. And it has recently been resurrected by scientists and their nuclear experiments.

Under its true but no less peculiar name of top quark, this shy subatomic behemoth isn't raging through Tokyo. Instead it's quietly leaving its tracks in huge underground detectors near Chicago. But like all good scientific discoveries, the top quark asks as many questions as it answers. Here are some of both.

The Reader's Digest Course in Subatomic Physics. Don't blink.

The success of science is its reductionism. If you don't understand something, cut it into smaller pieces until you find something you can understand. The search for subatomic particles, the smallest of all things, is the archetype of this process.

The atoms you learned about in high school chemistry---oxygen, hydrogen, carbon---are small, but they are not the smallest things. Atoms can be cut, or at least smashed, into their component electrons, protons, and neutrons. Protons and neutrons in turn are made of quarks, three apiece. Electrons and quarks, however, may be fundamental. No one has been able to subdivide them.

To spice up life, quarks come in different varieties or "flavors". The lightest and most common are up and down quarks, forming protons, neutrons, and thus us. Considerably heavier and much rarer are strange and charmed quarks. (The label "strange"---and physicists' predilection for peculiar nomenclature---can be traced to Caltech physicist Murray Gell-Mann, who also coined the quirky term "quark", which is taken from an obscure line from one of the most difficult books ever ostensibly written in the English language, Finnegan's Wake . I guess Gell-Mann was trying to prove something.)

Physicists catalog quarks in a ladder-like hierarchy, with the light up and down quarks on the first rung or generation, and the heavier strange and charmed quarks in the second generation. Now in addition to quarks the subatomic zoo includes leptons, the electron being one flavor of lepton. Like quarks, leptons are cataloged, pair-wise, into heavier and heaviest generations. By 1975 physicists had found three generations of leptons, six leptons in all. (The other leptons are the muon and tauon and the associated neutrinos.) When a fifth quark, the bottom, was discovered in 1977, it didn't take a rocket scientist to guess there was probably a sixth and final (maybe) quark to complete the third generation of quarks. The top.

How to Succeed in Particle Physics. By trying very, very hard. And by spending a lot of money.

For the past year [in 1995] rumors of sightings of the top quark have leaked out of Fermilab, the huge particle accelerator---atom-smasher---near Chicago. The official announcement came in April, 1995, after a seven year, billion-dollar search. It wasn't easy. At Fermilab protons race around at nearly the speed of light and then collide, head-on, producing showers of subatomic particles that are assiduously tracked and studied. From the tracks physicists deduce the kinds of particles forged in the collision. Out of 6 trillion collisions only forty top quarks were observed.

The top quark is rare because it is the biggest smallest thing yet to be found, outweighing the garden-variety up and down quarks in roughly the same proportion that Godzilla outweighs you and me. The energy required to produce this monster hasn't been seen since the Big Bang over 10 billion years ago.

But while finding the top quark fills a gap in the subatomic pantheon, the fat lady hasn't sung. Questions fall down like a Seattle rain:

Why do particles come in generations? And only three? Or are there more? And why, oh why, is the top quark so heavy?

The mass of the top quarks lies tangled up in the existence of another as-yet-undiscovered-but-believed-to-exist particle, the Higgs boson. The search for the Higgs was to have been the focus of the now-defunct Superconducting Supercollider, the $10 billion accelerator killed by Congress in 1994. Ten billion dollars is a lot of money, but the Higgs plays such a fundamental role that Nobel Laureate Leon Lederman nicknamed the Higgs "the God particle."

The Monster of the Id. Is the top quark worth a billion dollars? To taxpayers---I can't say. To particle physicists---undoubtedly. Melissa Franklin, first female professor of physics at Harvard and one of the discoverers of the top quark, quipped in a PBS interview that she "would rob banks" to fund her research.

Not out of greed. Not out of patriotism. Not out of a thirst for power, hoary sci-fi cliches to the contrary. But out of deep, unquenchable curiosity. Science formalizes this curiosity, and scientists pursue it with passion.

To some that passion can be unnerving (and let's be honest, in Franklin's case it especially unnerves some male scientists), to some merely expensive, to others monstrous. What I see, looming over the rooftops, is an enlargement of the fundamental questions, "But why?" that all children ask. Most stopped asking as they grew up. The rest became poets, revolutionaries, and scientists.

And that is what the top quark means to me.

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This essay first appeared, in slightly modified form, in the Seattle Weekly, July 19, 1995. It may not be copied or quoted in any form.