Improved measurement of the branching fraction of hc → γη′/η and search for hc → γπ0

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 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 R₇₂=B ({hc ⁰) }B ({hc ⁰ ^) }, 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 B B (h c → γπ 0) < 5. 0 × 10 − 5, at the 90% confidence level.