Three narrow resonances have been observed in e⁺e^- annihilation into hadrons at total energies between 9.4 and 10.4 GeV. Measurements of mass spacing and ratios of lepton pair widths support the interpretation of these "Υ" states as the lowest triplet-S levels of the bb̄ quark-antiquark system.
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Andrews et al. (1980) studied this question.
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