Oct. 29, 2005 In the universe of high-energy physics, the smallest building blocks of matter (or anti-matter) make the biggest news. Take subatomic particles, for instance. Colliding into each other at nearly the speed of light in the world’s highest-energy particle accelerator, protons and antiprotons produced some of the biggest physics news of the decade in 1995: the top quark.
The tenth anniversary of the discovery -- it was the last unknown particle of the six-member quark family predicted by current scientific theory -- is being celebrated by physicists around the world and at the Department of Energy’s Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, where the experiments took place inside the Tevatron, a four-mile long particle accelerator.
The discovery of the top quark, the result of a global collaboration among 74 universities, is particularly meaningful to Brandeis, whose high-energy physics group was deeply involved in the subatomic quest to find it. In a singular contribution, Milciades Contreras, then a doctoral student in physics, observed the first “top quark event” that led to its discovery.
“With a lot of enthusiasm I decided to go and search for the top quark, being quite aware that I was facing a once in a lifetime opportunity,” said Contreras. “One on occasion, while scanning data, I happened to find the first event seriously regarded as a top quark candidate – it was beautiful!”
Although Contreras could not claim discovery with only one recorded event, it provided the basis of his doctoral thesis and later became one of the two discovery channels for the top quark, explained Brandeis physicist Jim Bensinger.
“Discovering the top quark took many years and the work of hundreds of our collaborators who imagined, built and ran the experiment,” Contreras added.
In high-energy physics, observing a top quark, paired with its anti-top quark, is a fairly rare event, so enough experiments have to be run to statistically verify it is not other events. As Brandeis physicist Craig Blocker put it, “you have to get enough data to convince yourself you’ve seen it.”
Of course in physics, “seeing” takes on new meaning. In each of the 150 recorded top quark events that confirmed its discovery at Fermilab, neither the top nor bottom quark could actually be detected. Instead, computers graphically recorded the electronic signatures created by the various subatomic particles blasted apart in each collision. Once in a few billion collisions, physicists find the signature of top.
Since its discovery, the Brandeis group has been researching key questions about the properties of top and other particles. It’s all in pursuit of greater understanding of matter, energy, space and time, which particle physicists believe will help us understand how we got here and where we’re going.
Says Blocker: “We’re trying to understand how the universe works on a small scale.”
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