First observation of the M1 transition ψ(3686)→ γη_c(2S)

2012/05/24 by M. Ablikim, M. N. Achasov, D. J. Ambrose +356 · 1 citation
Physics and Astronomy · #hep-ex

paper · pdf · doi:10.1103/physrevlett.109.042003

7 pages, 1 figure, 1 table

arxiv created 2012/05/24 · arxiv updated 2014/08/05

Abstract

Using a sample of 106 million ψ(3686) events collected with the BESIII detector at the BEPCII storage ring, we have made the first measurement of the M1 transition between the radially excited charmonium S-wave spin-triplet and the radially excited S-wave spin-singlet states: ψ(3686)→γη_c(2S). Analyses of the processes ψ(2S)→ γη_c(2S) with η_c(2S)→ \K_S⁰ Kπand K⁺K^-π⁰ gave an η_c(2S) signal with a statistical significance of greater than 10 standard deviations under a wide range of assumptions about the signal and background properties. The data are used to obtain measurements of the η_c(2S) mass (M(η_c(2S))=3637.6± 2.9_stat± 1.6_sys MeV/c²), width (Γ(η_c(2S))=16.9± 6.4_stat± 4.8_sys MeV), and the product branching fraction (\BR(ψ(3686)→ γη_c(2S))× \BR(η_c(2S)→ K Kπ) = (1.30± 0.20_stat± 0.30_sys)× 10^-5). Combining our result with a BaBar measurement of \BR(η_c(2S)→ K K π), we find the branching fraction of the M1 transition to be \BR(ψ(3686)→γη_c(2S)) = (6.8± 1.1_stat± 4.5_sys)× 10^-4.

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