Single-γdecays ofη′(958),ω(783),φ(1019), andΞ*−(1535)

Abstract

We present direct evidence on single-$\gamma$ decays in which the $\gamma$ rays were converted to electron showers in tantalum plates or leaded-glass windows installed in the BNL 31-in. bubble chamber or in its 2 at.% neon-hydrogen filling. A > 90%-pure sample of 135 ${\eta }^{\prime }\to {\pi }^{+}{\pi }^{-}\gamma$ events is obtained. The Dalitz-plot projections show the $\rho$ meson and the sine-squared angular dependence clearly. The asymmetry between ${\pi }^{+}$ and ${\pi }^{-}$ mesons in the decay is found to be 0 ± 0.1. In addition, upper limits to the following decay modes are found: $({\eta }^{\prime }\to \omega \gamma )\le 0.05$, $(\omega \to {\pi }^{+}{\pi }^{-}\gamma )\le 0.06$, $(\phi \to {\pi }^{+}{\pi }^{-}\gamma )\le 0.06$, and ${\Xi }^{*-}\mathrm{}\left(1535\right)\mathrm{}\to {\Xi }^{-}\gamma \le 0.04$, all at the 90% confidence level.