Updated measurements of the M1 transition ψ (3686) →γηc (2S) with ηc (2S) →k K ¯ π

Abstract

Based on a data sample of (2712.4±14.3)×106ψ(3686) events collected with the BESIII detector at the BEPCII collider, the M1 transition ψ(3686)→γηc(2S) with ηc(2S)→KK̄π is studied, where KK̄π is K+K-π0 or KS0K±π∓. The mass and width of the ηc(2S) are measured to be (3637.8±0.8(stat)±0.2(syst)) MeV/c2 and (10.5±1.7(stat)±3.5(syst)) MeV, respectively. The product branching fraction B(ψ(3686)→γηc(2S))×B(ηc(2S)→KK̄π) is determined to be (0.97±0.06(stat)±0.09(syst))×10-5. Using B(ηc(2S)→KK̄π)=(1.86-0.49+0.68)%, we obtain the branching fraction of the radiative transition to be B(ψ(3686)→γηc(2S))=(5.2±0.3(stat)±0.5(syst)-1.4+1.9(extr))×10-4, where the third uncertainty is due to the quoted B(ηc(2S)→KK̄π).