We report evidence for the simultaneous production of $J/\psi$ and $\Upsilon$ mesons in 8.1 fb$^{ -1}$ of data collected at $\sqrt{ s}=$1.96 TeV by the D0 experiment at the Fermilab $p \bar p$ Tevatron Collider. Events with these characteristics are expected to be produced predominantly by gluon-gluon interactions. In this analysis, we extract the effective cross section characterizing the initial parton spatial distribution, $\sigma_{ eff}=2.2\pm 0.7\mbox{ (stat)} \pm 0.9 \mbox{ (syst)} ~\mbox{ mb}$.
Categories: hep-ex