Physicists at a European particle accelerator say they've spotted a never-before-seen elementary particle composed of five of the fundamental constituents known as quarks and antiquarks. In contrast, protons and neutrons contain three quarks, and no particle is known to have four quarks. The new report marks only the second sighting ever of a five-quark particle, the first one having been found last summer by three independent groups working in the United States, Japan, and Russia (SN: 7/5/03, p. 3: Wild Bunch: First five-quark particle turns up).
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