Observation of $\Upsilon(1S)$ pair production at CMS

The simultaneous production of two $\Upsilon(1S)$ mesons in proton-proton collisions is observed by CMS at $\sqrt s$ = 8 TeV at LHC in a data sample corresponding to an integrated luminosity of 20.7 fb$^{-1}$. The statistical significance is well in excess of 5 standard deviations. Both $\Upsilon$ candidates are fully reconstructed via their decays into $\mu^{+}\mu^{-}$. The acceptance region is defined by the individual $\Upsilon$ rapidity, $y(\Upsilon)$, and transverse momentum, $p_{T}(\Upsilon)$: $|y(\Upsilon)|$ $<$ 2.0 and $p_{T}(\Upsilon)<$ 50 GeV. The total cross section for the production of $\Upsilon(1S)$ pairs assuming that both $\Upsilon(1S)$ mesons decay isotropically, is measured to be 68.8 $\pm$ 12.7 (stat) $\pm$ 7.4 (syst) $\pm$ 2.8 (BR) pb, where the third uncertainty results from the uncertainty in the $\Upsilon(1S) \rightarrow \mu^{+}\mu^{-}$ branching fraction. Different assumptions about the $\Upsilon(1S)$ polarization imply modifications to the cross section ranging from -38\% to 36\%.