Search for double charmonium decays of the P-wave spin-triplet bottomonium states

Abstract

Using a sample of 158 million $Υ(2S)$ events collected with the Belle detector, we search for the first time for double charmonium decays of the $P$-wave spin-triplet bottomonium states ($Υ(2S) \to γχ_{bJ}$, $χ_{bJ} \to \jpsi \jpsi$, $\jpsi \psp$, $\psp \psp$ for J=0, 1, and 2). No significant $χ_{bJ}$ signal is observed in the double charmonium mass spectra, and we obtain the following upper limits, $\BR(χ_{bJ} \to \jpsi \jpsi)<7.1\times 10^{-5}$, $2.7\times 10^{-5}$, $4.5\times 10^{-5}$, $\BR(χ_{bJ} \to \jpsi \psp)<1.2\times 10^{-4}$, $1.7\times 10^{-5}$, $4.9\times 10^{-5}$, $\BR(χ_{bJ} \to \psp \psp)<3.1\times 10^{-5}$, $6.2\times 10^{-5}$, $1.6\times 10^{-5}$ 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.