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 "$\Upsilon$" states as the lowest triplet-$S$ levels of the $b\overline{b}$ quark-antiquark system.

• Received 15 February 1980

DOI:https://doi.org/10.1103/PhysRevLett.44.1108