In DepthParticle Physics

New pentaquarks hint at zoo of exotic matter

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Science  07 Jun 2019:
Vol. 364, Issue 6444, pp. 917
DOI: 10.1126/science.364.6444.917

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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.