We observe for the first time the process $e^{ +}e^{ -} \rightarrow \eta h_c$ with data collected by the BESIII experiment. Significant signals are observed at the center-of-mass energy $\sqrt{ s}=4.226$ GeV, and the Born cross section is measured to be $(9.5^{ +2.2}_{ -2.0} \pm 2.7)$ pb. Evidence for $\eta h_c$ is observed at $\sqrt{ s}=4.358$ GeV with a Born cross section of $(10.0^{ +3.1}_{ -2.7} \pm 2.6)$ pb, and upper limits on the production cross section at other center-of-mass energies between 4.085 and 4.600 GeV are determined.
Categories: hep-ex