Observation of $e^+ e^- \to ηY(2175)$ at center-of-mass energies above 3.7$\sim$GeV

Abstract

The state $Y(2175)$ is observed in the process $e^+ e^- \to ηY(2175)$ at center-of-mass energies between 3.7 and 4.6$\sim$GeV with a statistical significance larger than $10σ$ using data collected with the BESIII detector operating at the BEPCII storage ring. This is the first observation of the $Y(2175)$ in this process. The mass and width of the $Y(2175)$ are determined to be ($2135\pm 8\pm 9$)~MeV/$c^2$ and ($104\pm 24\pm 12$)~MeV, respectively, and the production cross section of $e^+ e^- \to ηY(2175)\to ηϕf_{0}(980)\to ηϕπ^+ π^-$ is at a several hundred femtobarn level. No significant signal for the process $e^+ e^- \to η' Y(2175)$ is observed and the upper limit on $σ(e^+ e^- \to η' Y(2175))/σ(e^+ e^- \to ηY(2175))$ is estimated to be 0.43 at the 90\% confidence level. We also search for $ψ(3686) \to ηY(2175)$. No significant signal is observed, indicating a strong suppression relative to the corresponding $J/ψ$ decay, in violation of the "12\% rule."