sciencehabit writes from a report via Science Magazine: Four years ago, when experimenters spotted pentaquarks — exotic, short-lived particles made of five quarks — some physicists thought they had glimpsed the strong nuclear force, which binds the atomic nucleus, engaging in a bizarre new trick. New observations have now expanded the zoo of pentaquarks, but suggest a tamer explanation for their structure. The findings, from the Large Hadron Collider beauty experiment (LHCb), a particle detector fed by the LHC at CERN, the European particle physics laboratory near Geneva, Switzerland, suggest pentaquarks are not bags of five quarks binding in a new way, but are more like conventional atomic nuclei, with a particle called a baryon that contains three quarks bound to another called a meson, which has two. Researchers say it’s too early to say which model of pentaquarks is correct, but the new observations move the needle toward the molecular picture. The study has been published in the journal Physical Review Letters.
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