Observation of Three Upsilon States

Abstract

Three narrow resonances have been observed in ${e}^{+}{e}^{\ensuremath{-}}$ 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 "$\ensuremath{\Upsilon}$" states as the lowest triplet-$S$ levels of the $b\overline{b}$ quark-antiquark system.