Search for the Radiative Transitions ψ(3770)→γη_c and γη_c(2S)

By using a 2.92 fb⁻¹ data sample taken at √s=3.773 GeV with the BESIII detector operating at the BEPCII collider, we search for the radiative transitions ψ(3770) → γη_c and γη_c(2S) through the hadronic decays η_c(η_c(2S)) → K_s^0 K^± π^∓. No significant excess of signal events above background is observed. We set upper limits at a 90% confidence level for the product branching fractions to be ℬ(ψ(3770)→γη_c) × ℬ(η_c→K_s^0 K^± π^∓) < 1.6×10⁻⁵ and ℬ(ψ(3770)→γη_c(2S)) × ℬ(η_c(2S)→K_s^0 K^± π^∓) < 5.6×10⁻⁶. Combining our result with world-average values of ℬ(η_c(η_c(2S))→K_s^0 K^± π^∓), we find the branching fractions ℬ(ψ(3770)→γη_c) < 6.8×10⁻⁴ and ℬ(ψ(3770)→γη_c(2S)) < 2.0×10⁻³ at a 90% confidence level.