Evidence for ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\gamma}{\ensuremath{\eta}}_{c}(1S)$ at center-of-mass energies between 4.01 and 4.60 GeV

Rapid Communication

Evidence for $e^{+} e^{-} \to γ η_{c} (1 S)$ at center-of-mass energies between 4.01 and 4.60 GeV

M. Ablikim et al. (BESIII Collaboration)

Phys. Rev. D 96, 051101(R) – Published 6 September 2017

Abstract

We present first evidence for the process $e^{+} e^{-} \to γ η_{c} (1 S)$ at six center-of-mass energies between 4.01 and 4.60 GeV using data collected by the BESIII experiment operating at BEPCII. We measure the Born cross section at each energy using a combination of twelve $η_{c} (1 S)$ decay channels. We also combine all six energies under various assumptions for the energy-dependence of the cross section. If the process is assumed to proceed via the $Y (4260)$ , we measure a peak Born cross section $σ_{peak} (e^{+} e^{-} \to γ η_{c} (1 S)) = 2.11 \pm 0.49 (stat .) \pm 0.36 (syst .) pb$ with a statistical significance of $4.2 σ$ .