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Pas de deux for a three-scoop particle

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2:09pm, July 2, 2007
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Two experiments running simultaneously at the Fermi National Accelerator Laboratory in Batavia, Ill., have observed a new particle called the cascade baryon. It is one of the most massive examples yet of a baryon—a class of particles made of three quarks held together by the strong nuclear force—and the first to contain one quark from each of the three known families, or generations, of these elementary particles.

Protons and neutrons are made of up and down quarks, the two first-generation quarks. Strange and charm quarks constitute the second generation, while the top and bottom varieties make up the third. Physicists had long conjectured that a down quark could combine with a strange and a bottom quark to form the three-generation cascade baryon.

On June 13, the scientists running DZero, one of two detectors at Fermilab's Tevatron accelerator, announced that they had detected characteristic showers of particles from the decay of cascade baryons. The baryons formed in proton-antiproton collisions and lived no more than a trillionth of a second. A week later, physicists at CDF, the Tevatron's other detector, reported their own sighting of the baryon.

DZero cospokesperson Dmitri Denisov says that measuring the lifetime and other properties of the cascade and other heavy baryons will help physicists refine their models of the strong nuclear force.

Recent improvements that have enabled the Tevatron to smash together protons and antiprotons in unprecedented numbers made possible the creation of the cascade baryon, he adds.

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