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

TL;DR

This paper reports the first experimental search for double-charmonium production in $(1S)$ and $(2S)$ decays, finding evidence for $(1S) ightarrow J/(3) + (4)$ and setting upper limits for other modes, consistent with theoretical predictions.

Contribution

First experimental evidence for $(1S) ightarrow J/(3)+(4)$ production and upper limits for other double-charmonium modes in $(1S)$ and $(2S)$ decays.

Findings

Evidence for $(1S) ightarrow J/(3)+(4)$ with $4.6\sigma$ significance.

Measured branching fraction for $(1S) ightarrow J/(3)+(4)$: $(3.90\pm1.21\pm0.23)\times10^{-6}$.

Upper limits on other modes are set at 90% confidence level.

Abstract

Using data samples of $102\times10^6$ $\Upsilon(1S)$ and $158\times10^6$ $\Upsilon(2S)$ events collected with the Belle detector, a first experimental search has been made for double-charmonium production in the exclusive decays $\Upsilon(1S,2S)\rightarrow J/\psi(\psi')+X$, 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 $\psi'$ except for the evidence of $\chi_{c1}$ production with a significance of $4.6\sigma$ for $\Upsilon(1S)\rightarrow J/\psi+\chi_{c1}$. The measured branching fraction $\BR(\Upsilon(1S)\rightarrow J/\psi+\chi_{c1})$ is $(3.90\pm1.21(\rm stat.)\pm0.23 (\rm syst.))\times10^{-6}$. 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.