Observation of X(2370) and search for X(2120) in J/ψ→γKK¯η′

Abstract

Using a sample of $1.31\times {10}^{9}J/\psi$ events collected with the BESIII detector, we perform a study of $J/\psi \to \gamma K\overline{K}{\eta }^{\prime }$. X(2370) is observed in the $K\overline{K}{\eta }^{\prime }$ invariant-mass distribution with a statistical significance of $8.3\sigma$. Its resonance parameters are measured to be $M=2341.6\pm 6.5\text{(stat.)}\pm 5.7\text{(syst.)}\text{MeV}/c^2$ and $\mathrm{\Gamma }=117\pm 10\text{(stat.)}\pm 8\text{(syst.)}\text{MeV}$. The product branching fractions for $J/\psi \to \gamma X(2370),X(2370)\to K^{+}{K}^{-}{\eta }^{\prime }$ and $J/\psi \to \gamma X(2370),X(2370)\to K_S^0{K}_S^0{\eta }^{\prime }$ are determined to be $(1.79\pm 0.23\text{(stat.)}\pm 0.65\text{(syst.)})\times {10}^{-5}$ and $(1.18\pm 0.32\text{(stat.)}\pm 0.39\text{(syst.)})\times {10}^{-5}$, respectively. No evident signal for X(2120) is observed in the $K\overline{K}{\eta }^{\prime }$ invariant-mass distribution. The upper limits for the product branching fractions of $\mathcal{B}(J/\psi \to \gamma X(2120)\to \gamma K^{+}{K}^{-}{\eta }^{\prime })$ and $\mathcal{B}(J/\psi \to \gamma X(2120)\to \gamma K_S^0{K}_S^0{\eta }^{\prime })$ are determined to be $1.49\times {10}^{-5}$ and $6.38\times {10}^{-6}$ at the 90% confidence level, respectively.