C. P. Shen, C. Z. Yuan, T. Iijima, Belle Collaboration
Using a sample of 158 million $\Upsilon(2S)$ events collected with the Belle detector, we search for the first time for double charmonium decays of the $P$-wave spin-triplet bottomonium states ($\Upsilon(2S) \to \gamma \chi_{bJ}$, $\chi_{bJ} \to \jpsi \jpsi$, $\jpsi \psp$, $\psp \psp$ for J=0, 1, and 2). No significant $\chi_{bJ}$ signal is observed in the double charmonium mass spectra, and we obtain the following upper limits, $\BR(\chi_{bJ} \to \jpsi \jpsi)<7.1\times 10^{-5}$, $2.7\times 10^{-5}$, $4.5\times 10^{-5}$, $\BR(\chi_{bJ} \to \jpsi \psp)<1.2\times 10^{-4}$, $1.7\times 10^{-5}$, $4.9\times 10^{-5}$, $\BR(\chi_{bJ} \to \psp \psp)<3.1\times 10^{-5}$, $6.2\times 10^{-5}$, $1.6\times 10^{-5}$ for J=0, 1, and 2, respectively, at the 90% confidence level. These limits are significantly lower than the central values (with uncertainties of 50% to 70%) predicted using the light cone formalism but are consistent with calculations using the NRQCD factorization approach.
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http://arxiv.org/abs/1203.0368
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