Observation and Spin-Parity Determination of the $X(1835)$ in $J/\ddot{I}ˆ\to {\hat{I}}^3{K}_S^0{K}_S^0\hat{I}\cdot$

Abstract

We report an observation of the process $J/\ddot{I}ˆ\to {\hat{I}}^{3}X(1835)\to {\hat{I}}^3{K}_S^0{K}_S^0\hat{I}\cdot$ at low $K_S^0{K}_S^0$ mass with a statistical significance larger than 12.9$\ddot{I}ƒ$ using a data sample of $1.31\times 10^9$ $J/\ddot{I}ˆ$ events collected with the BESIII detector. In this region of phase space the $K_S^0{K}_S^0$ system is dominantly produced through the $f_0(980)$. By performing a partial wave analysis, we determine the spin-parity of the $X(1835)$ to be $J^{PC}=0^{-+}$. The mass and width of the observed $X(1835)$ are $1844\pm 9(\text{stat}{)}_{-25}^{+16}(\text{syst})$~\MeV~and $192_{-17}^{+20}(\text{stat}{)}_{-43}^{+62}(\text{syst})$~MeV, respectively, which are consistent with the results obtained by BESIII in the channel $J/\ddot{I}ˆ\to {\hat{I}}^3\ddot{I}{€}^{+}\ddot{I}{€}^{-}\hat{I}{\cdot }^{\prime }$.

Final version published in PRL