Evidence of ${\rm Y}(1S)\to J/\psi +{\chi }_{c1}$ and search for double-charmonium production in ${\rm Y}(1S)$ and ${\rm Y}(2S)$ decays

Abstract

Using data samples of $102\times 10^6$ ${\rm Y}(1S)$ and $158\times 10^6$ ${\rm Y}(2S)$ events collected with the Belle detector, a first experimental search has been made for double-charmonium production in the exclusive decays ${\rm Y}(1S,2S)\to J/\psi ({\psi }^{\prime })+X$, where $X={\eta }_c$, ${\chi }_{cJ}(J=0,1,2)$, ${\eta }_c(2S)$, $X(3940)$, and $X(4160)$. No significant signal is observed in the spectra of the mass recoiling against the reconstructed $J/\psi$ or ${\psi }^{\prime }$ except for the evidence of ${\chi }_{c1}$ production with a significance of $4.6\sigma$ for ${\rm Y}(1S)\to J/\psi +{\chi }_{c1}$. The measured branching fraction $\text{BR}({\rm Y}(1S)\to J/\psi +{\chi }_{c1})$ is $(3.90\pm 1.21(stat.)\pm 0.23(syst.))\times 10^{-6}$. The $90\%$ confidence level upper limits on the branching fractions of the other modes having a significance of less than $3\sigma$ are determined. These results are consistent with theoretical calculations using the nonrelativistic QCD factorization approach.

Comments: 12 pages, 4 figures, 1 table. The fit range was extended to include X(4160) signal according to referee's suggestions. Other results unchanged. Paper was accepted for publication as a regular article in Physical Review D