Observation of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>ϒ</mml:mi></mml:mrow><mml:mrow><mml:mo>′</mml:mo><mml:mo>′</mml:mo><mml:mo>′</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>at the Cornell Electron Storage Ring

Abstract

During an energy scan at the Cornell Electron Storage Ring, with use of the Columbia University-Stony Brook NaI detector, an enhancement in $\ensuremath{\sigma}({e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\mathrm{hadrons})$ is observed at center-of-mass energy \ensuremath{\sim}10.55 GeV. The mass and leptonic width of this state (${\ensuremath{\Upsilon}}^{\ensuremath{'}\ensuremath{'}\ensuremath{'}}$) suggest that it is the $4^{3}S_{1}$ bound state of the $b$ quark and its antiquark. After applying to the data a cut in a (pseudo) thrust variable, the natural width is measured to be $\ensuremath{\Gamma}=12.6\ifmmode\pm\else\textpm\fi{}6.0$ MeV, indicating that the ${\ensuremath{\Upsilon}}^{\ensuremath{'}\ensuremath{'}\ensuremath{'}}$ is above the threshold for $B\overline{B}$ production.