Observation of a state $X(2600)$ in the ${\pi }^{+}{\pi }^{-}{\eta }^{\prime }$ system in the process $J/\psi \to \gamma {\pi }^{+}{\pi }^{-}{\eta }^{\prime }$

Abstract

Based on $(10087\pm 44)\times 10^6$ $J/\psi$ events collected with the BESIII detector, the process $J/\psi \to \gamma {\pi }^{+}{\pi }^{-}{\eta }^{\prime }$ is studied using two dominant decay channels of the ${\eta }^{\prime }$ meson, ${\eta }^{\prime }\to \gamma {\pi }^{+}{\pi }^{-}$ and ${\eta }^{\prime }\to \eta {\pi }^{+}{\pi }^{-},\eta \to \gamma \gamma$. The $X(2600)$ is observed with a statistical significance larger than 20$\sigma$ in the ${\pi }^{+}{\pi }^{-}{\eta }^{\prime }$ invariant mass spectrum, and it has a strong correlation to a structure around 1.5$\mathrm{GeV}$/{\it c}${}^2$ in the ${\pi }^{+}{\pi }^{-}$ invariant mass spectrum. A simultaneous fit on the ${\pi }^{+}{\pi }^{-}{\eta }^{\prime }$ and ${\pi }^{+}{\pi }^{-}$ invariant mass spectra with the two ${\eta }^{\prime }$ 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 $B(J/\psi \to \gamma X(2600))\cdot B(X(2600)\to f_0(1500){\eta }^{\prime })\cdot B(f_0(1500)\to {\pi }^{+}{\pi }^{-})$ = ($3.39\pm 0.18_{-0.66}^{+0.91})\times 10^{-5}$ and $B(J/\psi \to \gamma X(2600))\cdot B(X(2600)\to f_2^{{}^{\prime }}(1525){\eta }^{\prime })\cdot B(f_2^{{}^{\prime }}(1525)\to {\pi }^{+}{\pi }^{-})$ = ($2.43\pm 0.13_{-1.11}^{+0.31})\times 10^{-5}$, where the first uncertainties are statistical, and the second systematic.

8 pages, 2 figures

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• Towards the glueball spectrum from unquenched lattice QCD
• Decay of the pseudoscalar glueball into scalar and pseudoscalar mesons

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