Search for vector charmonium(-like) states in the $e^{+}{e}^{-}\to \eta J/\psi$ line shape

Abstract

The cross section of $e^{+}{e}^{-}\to \eta J/\psi$ has been measured by BESIII and Belle experiments. Fit to the $e^{+}{e}^{-}\to \eta J/\psi$ line shape, three resonant structures are evident. The parameters for the three resonant structures are $M_1=(3980\pm 17\pm 7)$ MeV/$c^2$, ${\Gamma }_1=(104\pm 32\pm 13)$ MeV; $M_2=(4219\pm 5\pm 4)$ MeV/$c^2$, ${\Gamma }_2=(63\pm 9\pm 3)$ MeV; $M_3=(4401\pm 12\pm 4)$ MeV/$c^2$, ${\Gamma }_3=(49\pm 19\pm 4)$ MeV, where the first uncertainties are statistical and the second systematic. We attribute the three structures to $\psi (4040)$, $Y(4220)$ and $\psi (4415)$ states. The branching fractions $\mathcal{B}(\psi (4040)\to \eta J/\psi )$ and $\mathcal{B}(\psi (4415)\to \eta J/\psi )$ are given. If $Y(4220)$ is taken as $\psi (4S)$ state, the branching fraction $\mathcal{B}(\psi (4S)\to \eta J/\psi )$ is also given. Combining all $Y(4220)$ parameters obtained from different decays, we give average parameters for $Y(4220)$, which are $M_{Y(4220)}=(4220.8\pm 2.4)$ MeV/$c^2$, ${\Gamma }_{Y(4220)}=(54.8\pm 3.3)$ MeV.