Search for charmonium and charmoniumlike states in ${\rm Y}(1S)$ radiative decays

Using a sample of $102\times {10}^6$ ${\rm Y}(1S)$ events collected with the Belle detector, we report on the first search for charge-parity-even charmonium and charmoniumlike states in ${\rm Y}(1S)$ radiative decays. No significant ${\chi }_{cJ}$ or ${\eta }_c$ signal is observed and 90% C.L. limits on $\mathcal{B}({\rm Y}(1S)\to \gamma {\chi }_{c0})<6.5\times {10}^{-4}$, $\mathcal{B}({\rm Y}(1S)\to \gamma {\chi }_{c1})<2.3\times {10}^{-5}$, $\mathcal{B}({\rm Y}(1S)\to \gamma {\chi }_{c2})<7.6\times {10}^{-6}$, and $\mathcal{B}({\rm Y}(1S)\to \gamma {\eta }_c)<5.7\times {10}^{-5}$ are obtained. The product branching fraction limits $\mathcal{B}({\rm Y}(1S)\to \gamma X(3872))\mathcal{B}(X(3872)\to {\pi }^{+}{\pi }^{-}J/\psi )<1.6\times {10}^{-6}$, $\mathcal{B}({\rm Y}(1S)\to \gamma X(3872))\mathcal{B}(X(3872)\to {\pi }^{+}{\pi }^{-}{\pi }^{0}J/\psi )<2.8\times {10}^{-6}$, $\mathcal{B}({\rm Y}(1S)\to \gamma X(3915))\mathcal{B}(X(3915)\to \omega J/\psi )<3.0\times {10}^{-6}$, and $\mathcal{B}({\rm Y}(1S)\to \gamma Y(4140))\mathcal{B}(Y(4140)\to \varphi J/\psi )<2.2\times {10}^{-6}$ are obtained at the 90% C.L. Furthermore, no evidence is found for excited charmonium states below $4.8\mathrm{GeV}/c^2$.

Figure 1

The ${\gamma }_{l}J/\psi$ invariant mass distribution in the ${\rm Y}(1S)$ data sample. Hints of ${\chi }_{c0}$ and ${\chi }_{c1}$ signals are seen, although no obvious ${\chi }_{c2}$ signal is observed. The solid curve is the best fit, the dashed curve is the background, and the shaded histogram is from the normalized $J/\psi$ mass sidebands.

Figure 2

The mass distribution for a sum of the five ${\eta }_c$ decay modes. The solid line is a sum of the corresponding functions obtained from a simultaneous fit to all the ${\eta }_c$ decay modes, and the dashed line is a sum of the background functions from the fit. The shaded histogram is a sum of the normalized continuum events, where the $J/\psi$ signal is produced via ISR.

Figure 3

(a) Distribution of the ${\pi }^{+}{\pi }^{-}J/\psi$ invariant mass for ${\rm Y}(1S)\to \gamma {\pi }^{+}{\pi }^{-}J/\psi$ candidates. (b) Distribution of the ${\pi }^{+}{\pi }^{-}{\pi }^{0}J/\psi$ invariant mass for ${\rm Y}(1S)\to \gamma {\pi }^{+}{\pi }^{-}{\pi }^{0}J/\psi$ candidates. Points with error bars are data, and open histograms are the MC expectation for the $X(3872)$ signal (not normalized). The peak at $3.686\mathrm{GeV}/c^2$ in (a) is due to $\psi (2S)$ production via ISR.