Observation of a state $X(2600)$ in the $\ddot{I}{€}^{+}\ddot{I}{€}^{-}\hat{I}{\cdot }^{\prime }$ system in the process $J/\ddot{I}ˆ\to {\hat{I}}^3\ddot{I}{€}^{+}\ddot{I}{€}^{-}\hat{I}{\cdot }^{\prime }$

Abstract

Based on $(10087\pm 44)\times 10^6$ $J/\ddot{I}ˆ$ events collected with the BESIII detector, the process $J/\ddot{I}ˆ\to {\hat{I}}^3\ddot{I}{€}^{+}\ddot{I}{€}^{-}\hat{I}{\cdot }^{\prime }$ is studied using two dominant decay channels of the $\hat{I}{\cdot }^{\prime }$ meson, $\hat{I}{\cdot }^{\prime }\to {\hat{I}}^3\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ and $\hat{I}{\cdot }^{\prime }\to \hat{I}\cdot \ddot{I}{€}^{+}\ddot{I}{€}^{-},\hat{I}\cdot \to {\hat{I}}^3{\hat{I}}^3$. The $X(2600)$ is observed with a statistical significance larger than 20$\ddot{I}ƒ$ in the $\ddot{I}{€}^{+}\ddot{I}{€}^{-}\hat{I}{\cdot }^{\prime }$ invariant mass spectrum, and it has a strong correlation to a structure around 1.5$\mathrm{GeV}$/{\it c}${}^2$ in the $\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ invariant mass spectrum. A simultaneous fit on the $\ddot{I}{€}^{+}\ddot{I}{€}^{-}\hat{I}{\cdot }^{\prime }$ and $\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ invariant mass spectra with the two $\hat{I}{\cdot }^{\prime }$ decay modes indicates that the mass and width of the $X(2600)$ state are $2617.8\pm 2.1_{-1.9}^{+18.2}\mathrm{MeV}$/{\it c}${}^2$ and $200\pm 8_{-17}^{+20}\mathrm{MeV}$, respectively. The corresponding branching fractions are measured to be $B(J/\ddot{I}ˆ\to {\hat{I}}^{3}X(2600))\cdot B(X(2600)\to f_0(1500)\hat{I}{\cdot }^{\prime })\cdot B(f_0(1500)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-})$ = ($3.39\pm 0.18_{-0.66}^{+0.91})\times 10^{-5}$ and $B(J/\ddot{I}ˆ\to {\hat{I}}^{3}X(2600))\cdot B(X(2600)\to f_2^{{}^{\prime }}(1525)\hat{I}{\cdot }^{\prime })\cdot B(f_2^{{}^{\prime }}(1525)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-})$ = ($2.43\pm 0.13_{-1.11}^{+0.31})\times 10^{-5}$, where the first uncertainties are statistical, and the second systematic.

8 pages, 2 figures