Sequential Decays of the Υ″

Abstract

We have studied the decay chain \ensuremath{\Upsilon}\ensuremath{''}\ensuremath{\rightarrow}${\mathrm{\ensuremath{\chi}}}_{\mathrm{b}}^{\ensuremath{'}}$(${\mathrm{\ensuremath{\chi}}}_{\mathrm{b}}$)\ensuremath{\gamma}\ensuremath{\rightarrow}\ensuremath{\Upsilon}\ensuremath{'}(\ensuremath{\Upsilon})\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\mu}(ee)\ensuremath{\gamma}\ensuremath{\gamma}with the CUSB II detector at the Cornell Electron Storage Ring. For a sample of 1.33\ifmmode\times\else\texttimes\fi{}${10}^{6}$ \ensuremath{\Upsilon}\ensuremath{''}'s we find \ensuremath{\approx}400 events. We measure branching ratios for${\mathrm{\ensuremath{\chi}}}_{\mathrm{bJ}}^{\ensuremath{'}}$\ensuremath{\rightarrow}\ensuremath{\Upsilon}\ensuremath{'}(\ensuremath{\Upsilon})\ensuremath{\gamma} and, using calculated E1 rates, we derive total and hadronic widths of the${\mathrm{\ensuremath{\chi}}}_{\mathrm{b}}^{\ensuremath{'}}$ states. From these widths we obtain values of ${\mathrm{a}}_{\mathrm{s}}$ in the range between 0.13 and 0.21, in agreement with other determinations. We observe the suppressed decay \ensuremath{\Upsilon}\ensuremath{''}\ensuremath{\rightarrow}${\mathrm{\ensuremath{\chi}}}_{\mathrm{b}}$\ensuremath{\gamma}. The measured branching ratio suggests that relativistic effects are important. We also determine the branching ratios for \ensuremath{\Upsilon}\ensuremath{''}\ensuremath{\rightarrow}\ensuremath{\Upsilon}\ensuremath{'}${\mathrm{\ensuremath{\pi}}}^{0}$${\mathrm{\ensuremath{\pi}}}^{0}$ to be (1.3\ifmmode\pm\else\textpm\fi{}0.4\ifmmode\pm\else\textpm\fi{}0.2)% and\ensuremath{\Upsilon}\ensuremath{''}\ensuremath{\rightarrow}\ensuremath{\Upsilon}${\mathrm{\ensuremath{\pi}}}^{0}$${\mathrm{\ensuremath{\pi}}}^{0}$ to be (1.8\ifmmode\pm\else\textpm\fi{}0.3\ifmmode\pm\else\textpm\fi{}0.2)%. \textcopyright{} 1991 The American Phsyical Society