First observation of the $M1$ transition $\psi(3686) \rightarrow \gamma\eta_c (2S)$

Le résumé fourni par la source

Using a sample of $106×10^6$ $\\psi(3686)$ 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: $\\psi(3686)→\\gamma\\eta_c (2S)$. Analyses of the processes $\\psi(3686)→\\gamma\\eta_c (2S)$ with $\\eta_c (2S)→K^{0}_{S} K^{±}\\pi^∓$ and $K^+K^−\\pi^0$ give an $\\eta_c (2S)$ 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 $\\eta_c (2S)$ mass $(M(\\eta_c (2S))=3637.6±2.9_{\\text{stat}}±1.6_{\\text{syst}} MeV/c^2)$, width $(\\Gamma(\\eta_c (2S))=16.9±6.4_{\\text{stat}}±4.8_{\\text{syst}} MeV)$, and the product branching-fraction $(\\mathscr{B}(\\psi(3686)→\\gamma\\eta_c (2S))×\\mathscr{B}(\\eta_c (2S)→K\\overline{K}_π)=(1.30±0.20_{stat}±0.30_{\\text{syst}})×10^{−5})$. Combining our result with a BABAR measurement of $\\mathscr{B}(\\eta_c (2S)→K\\overline{K}_π)$, we find the branching fraction of the $M1$ transition to be $\\mathscr{B}(\\psi(3686)→\\gamma\\eta_c (2S))=(6.8±1.1_{\\text{stat}}±4.5_{\\text{syst}})×10^{−4}$.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.