Search for ${\eta }_c^{\prime }$ decays into vector meson pairs

The processes ${\eta }_c^{\prime }\to {\rho }^0{\rho }^0$, $K^{*0}{\overline{K}}^{*0}$, and $\varphi \varphi$ are searched for using a sample of $1.06\times {10}^8$ ${\psi }^{\prime }$ events collected with the BESIII detector at the BEPCII collider. No signals are observed in any of the three final states. The upper limits on the decay branching fractions are determined to be $\mathcal{B}({\eta }_c^{\prime }\to {\rho }^0{\rho }^0)<3.1\times {10}^{-3}$, $\mathcal{B}({\eta }_c^{\prime }\to K^{*0}{\overline{K}}^{*0})<5.4\times {10}^{-3}$, and $\mathcal{B}({\eta }_c^{\prime }\to \varphi \varphi )<2.0\times {10}^{-3}$ at the 90% confidence level. The upper limits are lower than the existing theoretical predictions.

Figure 1

Comparison between $3C$ and $4C$ kinematic fits (unnormalized). Shown in the plot are the signal with the $3C$ fit (filled circles), signal with the $4C$ fit (open circles), ${\psi }^{\prime }\to X$ background with the $3C$ fit (solid line), and ${\psi }^{\prime }\to X$ background with the $4C$ fit (dashed line).

Figure 2

The measured background from ${\psi }^{\prime }\to {\pi }^{0}X$ events (dots with error bars) for the modes (a) $\gamma {\rho }^0{\rho }^0$ and (b) $\gamma K^{*0}{\overline{K}}^{*0}$. The curves show the best fit with Novosibirsk functions.

Figure 3

The two-dimensional plots of $M_X^{3C}$ versus $M_{{\gamma }_{\mathrm{FSR}}X}^{3C}$ for events passing the ${\psi }^{\prime }\to \gamma {\gamma }_{\mathrm{FSR}}X$ selection with $X=2({\pi }^{+}{\pi }^{-})$. From left to right they are (a) MC simulated ${\chi }_{c0}$ signal, (b) inclusive MC, and (c) data. In each plot the dashed-line and the solid-line boxes contain events without and with a FSR photon, respectively. MC simulations reproduce the shape well but not the amount of FSR events.

Figure 4

Invariant mass distributions of the vector meson pairs after a $3C$ kinematic fit for the modes: (a) ${\rho }^0{\rho }^0$, (b) $K^{*0}{\overline{K}}^{*0}$, and (c) $\varphi \varphi$. Dots with error bars are data, and the solid curves in (a) and (b) are from the best fit to the mass spectra. No fit is performed for (c) due to low statistics. In (a) and (b), the ${\eta }_c^{\prime }$ signals are shown as short dashed lines, ${\psi }^{\prime }\to {\pi }^{0}X$ backgrounds are in dotted lines, continuum in long dashed lines, and ${\psi }^{\prime }\to ({\gamma }_{\mathrm{FSR}})X$ in short dash-dot-dotted lines.