Observation of a vector charmoniumlike state in $e^{+}{e}^{-}\to D_s^{+}{D}_{s1}(2536{)}^{-}+c.c.$

Abstract

Using a data sample of 921.9 fb${}^{-1}$ collected with the Belle detector, we study the process of $e^{+}{e}^{-}\to D_s^{+}{D}_{s1}(2536{)}^{-}+c.c.$ via initial-state radiation. We report the first observation of a vector charmoniumlike state decaying to $D_s^{+}{D}_{s1}(2536{)}^{-}+c.c.$ with a significance of 5.9$\sigma$, including the systematic uncertainties. The measured mass and width are $(4625.9_{-6.0}^{+6.2}(stat.)\pm 0.4(syst.))\mathrm{MeV}/c^2$ and $(49.8_{-11.5}^{+13.9}(stat.)\pm 4.0(syst.))\mathrm{MeV}$, respectively. The product of the $e^{+}{e}^{-}\to D_s^{+}{D}_{s1}(2536{)}^{-}+c.c.$ cross section and the branching fraction of $D_{s1}(2536{)}^{-}\to {\bar{D}}^{\ast 0}{K}^{-}$ is measured from the $D_s{\bar{D}}_{s1}(2536)$ threshold to 5.59~GeV.

Comments: 8 pages, 3 figures, plus 2 pages Supplemental Material