Magazine article Science News

Extra Data Bolster Top Quark Discovery

Magazine article Science News

Extra Data Bolster Top Quark Discovery

Article excerpt

The top quark's true identity is beginning to emerge from the debris of trillions of high-energy collisions between protons and their antimatter counterparts.

Last year, physicists at the Fermi National Accelerator Laboratory (Fermilab) in Batavia, Ill., presented the first direct experimental evidence for the existence of the long-sought top quark (SN: 4/30/94, p.276). But significant uncertainties in the limited data available rendered the results suspect.

Now, after acquiring and sifting through three times as much data, Fermilab researchers are confident that they have indeed discovered the top quark. Moreover, teams using two different detectors have observed traces of this elusive subatomic particle. A year ago, only the group using the Collider Detector at Fermilab (CDF) claimed any sightings.

At that time, researchers at the rival DZero detector "just did not have enough events to make a statement about the top quark's existence, but now, with a larger data sample, the signal is clear," says Paul D. Grannis of the State University of New York at Stony Brook, a DZero team member.

Representatives of the CDF and DZero teams reported their findings at a seminar held last week at Fermilab.

According to the standard model of particle physics, quarks come in six varieties. Two kinds of quarks -- known as up and down quarks -- combine to create the protons and neutrons of everyday matter. Three other types of quarks -- strange, charm, and bottom -- have been found using particle accelerators. The newly discovered top quark completes the family.

Created as quark-antiquark pairs in collisions between protons and antiprotons moving at nearly the speed of light, top quarks disintegrate almost immediately to create characteristic showers of other particles that physicists can then detect. However, because decays of other subatomic particles can mimic those postulated for the top quark, researchers must take care to distinguish these "background" events from genuine top quark decays. …

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