The Discovery of the Top Quark [From the Archive]

Finding the sixth quark involved the world's most energetic collisions and a cast of thousands

Join Our Community of Science Lovers!

Editor's note: This article was originally published in the September 1997 issue of Scientific American (a PDF version of the original is available for purchase below). We have resurfaced this article to commemorate the end of the Tevatron.

In March 1995 scientists gathered at a hastily called meeting at Fermilab—the Fermi National Accelerator Laboratory in Batavia, Ill., near Chicago—to witness a historic event. In back-to-back seminars, physicists from rival experiments within the lab announced the discovery of a new particle, the top quark. A decades-long search for one of the last missing pieces in the Standard Model of particle physics had come to an end.

The top quark is the sixth, and quite possibly the last, quark. Along with leptons—the electron and its relativesquarks are the building blocks of matter. The lightest quarks, designated “up” and “down,” make up the familiar protons and neutrons. Along with the electrons, these make up the entire periodic table. Heavier quarks (such as the charm, strange, top and bottom quarks) and leptons, though abundant in the early moments after the big bang, are now commonly produced only in accelerators. The Standard Model describes the interactions among these building blocks. It requires that leptons and quarks each come in pairs, often called generations.

On supporting science journalism

If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

Physicists had known that the top must exist since 1977, when its partner, the bottom, was discovered. But the top proved exasperatingly hard to find. Although a fundamental particle with no discernible structure, the top quark turns out to have a mass of 175 billion electron volts (GeV)—as much as an atom of gold and far greater than most theorists had anticipated. The proton, made of two ups and one down, has a mass of just under 1 GeV. (The electron volt is a unit of energy, related to mass via E = mc².)

Subscribe Buy This Issue

Already a Digital subscriber? Sign-in Now

If your institution has site license access, enter here.

It’s Time to Stand Up for Science

If you enjoyed this article, I’d like to ask for your support. Scientific American has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history.

I’ve been a Scientific American subscriber since I was 12 years old, and it helped shape the way I look at the world. SciAm always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does that for you, too.

If you subscribe to Scientific American, you help ensure that our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten labs across the U.S.; and that we support both budding and working scientists at a time when the value of science itself too often goes unrecognized.

In return, you get essential news, captivating podcasts, brilliant infographics, can't-miss newsletters, must-watch videos, challenging games, and the science world's best writing and reporting. You can even gift someone a subscription.

There has never been a more important time for us to stand up and show why science matters. I hope you’ll support us in that mission.

Thank you,

David M. Ewalt, Editor in Chief, Scientific American