The invariant mass spectrum of the ${\eta }^{\prime }{\pi }^{+}{\pi }^{-}$ final state produced in two-photon collisions is obtained using a $673{\mathrm{fb}}^{-1}$ data sample collected in the vicinity of the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We observe a clear signal of the ${\eta }_c(1S)$ and measure its mass and width to be $M({\eta }_c(1S))=(2982.7\pm 1.8(\mathrm{stat})\pm 2.2(\mathrm{syst})\pm 0.3(\mathrm{\text{model}}))\mathrm{MeV}/c^2$ and $\Gamma ({\eta }_c(1S))=({37.8}_{-5.3}^{+5.8}(\mathrm{stat})\pm 2.8(\mathrm{syst})\pm 1.4(\mathrm{\text{model}}))\mathrm{MeV}/c^2$. The third error is an uncertainty due to possible interference between the ${\eta }_c(1S)$ and a nonresonant component. We also report the first evidence for $\eta (1760)$ decay to ${\eta }^{\prime }{\pi }^{+}{\pi }^{-}$; we find two solutions for its parameters, depending on the inclusion or not of the $X(1835)$, whose existence is of marginal significance in our data. From a fit to the mass spectrum using coherent $X(1835)$ and $\eta (1760)$ resonant amplitudes, we set a 90% confidence level upper limit on the product ${\Gamma }_{\gamma \gamma }\mathcal{B}({\eta }^{\prime }{\pi }^{+}{\pi }^{-})$ for the $X(1835)$.

• Received 23 June 2012

DOI:https://doi.org/10.1103/PhysRevD.86.052002