Evidence for ${\ensuremath{\eta}}_{c}(2S)$ in $\ensuremath{\psi}(3686)\ensuremath{\rightarrow}\ensuremath{\gamma}{K}_{S}^{0}{K}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\pi}}^{\ensuremath{\mp}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$

Evidence for $η_{c} (2 S)$ in $ψ (3686) \to γ K_{S}^{0} K^{\pm} π^{\mp} π^{+} π^{-}$

M. Ablikim et al. (BESIII Collaboration)

Phys. Rev. D 87, 052005 – Published 4 March 2013

Abstract

We search for the M1 radiative transition $ψ (3686) \to γ η_{c} (2 S)$ by reconstructing the exclusive $η_{c} (2 S) \to K_{S}^{0} K^{\pm} π^{\mp} π^{+} π^{-}$ decay using $1.06 \times 10^{8}$ $ψ (3686)$ events collected with the BESIII detector. The signal is observed with a statistical significance of greater than 4 standard deviations. The measured mass of the $η_{c} (2 S)$ is $3646.9 \pm 1.6 (stat) \pm 3.6 (syst) MeV / c^{2}$ , and the width is $9.9 \pm 4.8 (stat) \pm 2.9 (syst) MeV / c^{2}$ . The product branching fraction is measured to be $B (ψ (3686) \to γ η_{c} (2 S)) \times B (η_{c} (2 S) \to K_{S}^{0} K^{\pm} π^{\mp} π^{+} π^{-}) = (7.03 \pm 2.10 (stat) \pm 0.70 (syst)) \times 10^{- 6}$ . This measurement complements a previous BESIII measurement of $ψ (3686) \to γ η_{c} (2 S)$ with $η_{c} (2 S) \to K_{S}^{0} K^{\pm} π^{\mp}$ and $K^{+} K^{-} π^{0}$ .