Observation of theηc(2980) Produced in the Radiative Decay of theψ′(3684)

Abstract

In a study of ${\psi }^{\prime }$ (3684) radiative decays with the Mark II detector at SPEAR, the decay sequence ${\psi }^{\prime }\to \gamma {\eta }_c$ (2980) is observed, with the ${\eta }_c$ (2980) decaying into several completely reconstructed hadronic modes. A mass $M=2980\mathrm{}\pm 8$ ${\mathrm{M}\mathrm{e}\mathrm{V}/\mathit{c}}^2$ and a width $\Gamma <40\mathrm{}$ ${\mathrm{M}\mathrm{e}\mathrm{V}/\mathit{c}}^2$ (90%) confidence level) are obtained, and estimates of some of the decay branching ratios are presented.