Measurement of double charmonium production in $e^{+}{e}^{-}$ annihilations at $\sqrt{s}=10.6\mathrm{GeV}$

We study $e^{+}{e}^{-}\to J/\psi c\overline{c}$ by measuring the invariant mass distribution recoiling against fully reconstructed $J/\psi$ decays, using $124{\mathrm{fb}}^{-1}$ of data collected at a center-of-mass energy of 10.6 GeV with the BABAR detector. We observe signals for ${\eta }_c(1S)$, ${\chi }_{c0}$, and ${\eta }_c(2S)$ in the recoil mass distribution, thus confirming previous measurements. We measure $\sigma (e^{+}{e}^{-}\to J/\psi +c\overline{c})\mathcal{B}(c\overline{c}\to >2\mathrm{\text{charged}})$ to be $17.6\pm 2.8{(\mathrm{stat})}_{-2.1}^{+1.5}(\mathrm{syst})\mathrm{fb}$, $10.3\pm 2.5{(\mathrm{\text{stat}})}_{-1.8}^{+1.4}(\mathrm{\text{syst}})\mathrm{fb}$, and $16.4\pm 3.7{(\mathrm{\text{stat}})}_{-3.0}^{+2.4}(\mathrm{\text{syst}})\mathrm{fb}$ with $c\overline{c}={\eta }_c(1S)$, ${\chi }_{c0}$, and ${\eta }_c(2S)$, respectively.

Figure 1

Distributions of (a) $\cos {\theta }_l$ and (b) $E_{\mathrm{QED}}-E_{\mathrm{beams}}$ in the data, (c) $\cos {\theta }_l$ and (d) $E_{\mathrm{QED}}-E_{\mathrm{beams}}$ in the signal Monte Carlo. The arrows point to where the selection criteria are applied.

Figure 2

The fit to the recoil mass distribution is represented by the solid curve. The dashed curve is a second-order polynomial representing the background. The points with error bars refer to the events in the $J/\psi$ mass window. The histograms represent different sources of backgrounds.