Popis: |
133 pp. (1986). The cascade reaction $e^+e^- \to \Upsilon' \to \gamma X_b \to \gamma \gamma \Upsilon \to \gamma \gamma (\mu^+ \mu^-$ or $e^+e^-)$ has been studied with the Crystal Ball detector at the $e^+e^-$ storage ring DORIS-II. Two $x_b$ states are observed by monoenergetic photon lines at 107.7 ± 1.1 ± 1.0 MeV and 132.4 ± 0.9 ± 1.0 MeV, with amplitudes of 56 ± 6 and 82 ± 10 events correspondingly. Upper limits for full widths of those states at 90 % confidence level are < 6.2 MeV and < 6.9 MeV respectively... |