Branching-fraction measurements of $\psi (2S)$ decay to baryon-antibaryon final states

Using $3.08\times {10}^6$ $\psi (2S)$ decays observed in $e^{+}{e}^{-}$ collisions by the CLEO detector, we present the results of a study of the $\psi (2S)$ decaying into baryon-antibaryon final states. We report the most precise measurements of the following eight modes: $p\overline{p}$, $\Lambda \overline{\Lambda }$, ${\Sigma }^{+}\overline{{\Sigma }^{+}}$ (first observation), ${\Sigma }^0\overline{{\Sigma }^0}$, ${\Xi }^{-}\overline{{\Xi }^{-}}$, and ${\Xi }^0\overline{{\Xi }^0}$ (first observation), and place upper limits for the modes $\Xi (1530{)}^0\overline{\Xi (1530{)}^0}$ and ${\Omega }^{-}\overline{{\Omega }^{-}}$.

Figure 1

Inclusive hyperon invariant mass distribution in $\psi (2S)$ data: (a) $\Lambda \to p{\pi }^{-}$, (b) ${\Sigma }^{+}\to p{\pi }^0$, (c) ${\Sigma }^0\to \gamma \Lambda$, (d) ${\Xi }^{-}\to \Lambda {\pi }^{-}$, (e) ${\Xi }^0\to \Lambda {\pi }^0$, (f) $\Xi (1530{)}^0\to {\Xi }^{-}{\pi }^{+}$, (g) ${\Omega }^{-}\to \Lambda K^{-}$.

Figure 2

Scaled energy ($E_{\mathrm{vis}}/\sqrt{s}$) distribution for eight $\psi (2S)$ decay modes: (a) $p\overline{p}$, (b) $\Lambda \overline{\Lambda }$, (c) ${\Sigma }^{+}\overline{{\Sigma }^{+}}$, (d) ${\Sigma }^0\overline{{\Sigma }^0}$, (e) ${\Xi }^{-}\overline{{\Xi }^{-}}$, (f) ${\Xi }^0\overline{{\Xi }^0}$, (g) ${\Xi }^0\overline{{\Xi }^0}$, and (h) ${\Omega }^{-}\overline{{\Omega }^{-}}$. Signal Monte Carlo, data, and scaled continuum plots are shown in solid line, error bar, and filled histograms, respectively.

Figure 3

(a) Reduced branching fractions $|M_i{|}^2$ for $\mathcal{B}(\psi (2S)\to B_i\overline{B_i})/(\pi p^{*}/\sqrt{s})$ for $\psi (2S)\to$ baryon-antibaryon decays. (b) Comparison of $\mathcal{B}(\psi (2S)\to B_i\overline{B_i})$ to Boltz and Kroll’s predictions from perturbative QCD. Horizontal line is ${\Gamma }_{\exp }/{\Gamma }_{\mathrm{qcd}}=1.0$.