The mass $m_{{\eta }_c}$ and total width ${\Gamma }_{\mathrm{tot}}^{{\eta }_c}$ of the ${\eta }_c$ meson have been measured in two-photon interactions at the SLAC $e^{+}{e}^{-}$ asymmetric $B$ Factory with the BABAR detector. With a sample of approximately 2500 reconstructed ${\eta }_c\to K_S^0{K}^{\pm }{\pi }^{\mp }$ decays in $88{\mathrm{fb}}^{-1}$ of data, the results are $m_{{\eta }_c}=2982.5\pm 1.1(\mathrm{stat})\pm 0.9(\mathrm{syst})\mathrm{MeV}/c^2$ and ${\Gamma }_{\mathrm{tot}}^{{\eta }_c}=34.3\pm 2.3(\mathrm{stat})\pm 0.9(\mathrm{syst})\mathrm{MeV}/c^2$. Using the same decay mode, a second resonance with $112\pm 24$ events is observed with a mass of $3630.8\pm 3.4(\mathrm{stat})\pm 1.0(\mathrm{syst})\mathrm{MeV}/c^2$ and width of $17.0\pm 8.3(\mathrm{stat})\pm 2.5(\mathrm{syst})\mathrm{MeV}/c^2$. This observation is consistent with expectations for the ${\eta }_c(2S)$ state.

• Received 18 November 2003

DOI:https://doi.org/10.1103/PhysRevLett.92.142002