Abstract

A bstract The processes h c → γP ( P = η ′ , η, π 0 ) are studied with a sample of (27 . 12 ± 0 . 14) × 10 8 ψ (3686) events collected by the BESIII detector at the BEPCII collider. The decay h c → γη is observed for the first time with the significance of 9 . 0 σ , and the branching fraction is determined to be (3 . 77 ± 0 . 55 ± 0 . 13 ± 0 . 26) × 10 − 4 , while $$ \mathcal{B} $$ B ( h c → γη ′) is measured to be (1 . 40 ± 0 . 11 ± 0 . 04 ± 0 . 10) × 10 − 3 , where the first uncertainties are statistical, the second systematic, and the third from the branching fraction of ψ (3686) → π 0 h c . The combination of these results allows for a precise determination of $$ {R}_{h_c}=\frac{\mathcal{B}\left({h}_c\to {\pi}^0\gamma \eta \right)}{\mathcal{B}\left({h}_c\to {\pi}^0\gamma {\eta}^{\prime}\right)}, $$ R h c = B h c → γη B h c → γ η ′ , which is calculated to be (27 . 0 ± 4 . 4 ± 1 . 0)%. The results are valuable for gaining a deeper understanding of η − η ′ mixing, and its manifestation within quantum chromodynamics. No significant signal is found for the decay h c → γπ 0 , and an upper limit is placed on its branching fraction of $$ \mathcal{B} $$ B ( h c → γπ 0 ) < 5 . 0 × 10 − 5 , at the 90% confidence level.