Observation of the UPSILON''' at the Cornell electron-storage ring

During an energy scan at the Cornell Electron Storage Ring, with use of the Columbia University-Stony Brook NaI detector, an enhancement in sigma(e/sup +/e/sup -/..-->..hadrons) is observed at center-of-mass energy approx.10.55 GeV. The mass and leptonic width of this state (UPSILON''') suggest that it is the 4 /sup 3/S/sub 1/ bound state of the b quark and its anitquark. After applying to the data a cut in a (pseudo) thrust variable, the natural width is measured to be GAMMA=12.6 +- 6.0 MeV, indicating that the UPSILON''' is above the threshold for BB-bar production.