Observation of e+e−→ηY(2175) at center-of-mass energies above 3.7 GeV

The state $Y(2175)$ is observed in the process $e^{+}{e}^{-}\to \eta Y(2175)$ with a statistical significance larger than 10 standard deviations using the data collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies between 3.7 and 4.6 GeV. This is the first observation of the $Y(2175)$ in this process. The mass and width of the $Y(2175)$ are determined to be $(2135\pm 8\pm 9)\mathrm{MeV}/c^2$ and $(104\pm 24\pm 12)\mathrm{MeV}$, respectively, and the production cross section ($\sigma$) of $e^{+}{e}^{-}\to \eta Y(2175)\to \eta \varphi f_0(980)\to \eta \varphi {\pi }^{+}{\pi }^{-}$ is at the several hundred femtobarn level. No significant signal for the process $e^{+}{e}^{-}\to {\eta }^{\prime }Y(2175)$ is observed and the upper limit on $\sigma (e^{+}{e}^{-}\to {\eta }^{\prime }Y(2175))/\sigma (e^{+}{e}^{-}\to \eta Y(2175))$ is estimated to be 0.43 at the 90% confidence level. We also search for $\psi (3686)\to \eta Y(2175)$. No significant signal is observed, indicating a strong suppression relative to the corresponding $J/\psi$ decay, in violation of the “12% rule”.