Evidence for Simultaneous Production of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>J</mml:mi><mml:mo stretchy="false">/</mml:mo><mml:mi>ψ</mml:mi></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">ϒ</mml:mi></mml:mrow></mml:math>Mesons

We report evidence for the simultaneous production of $J/\ensuremath{\psi}$ and $\mathrm{\ensuremath{\Upsilon}}$ mesons in $8.1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data collected at $\sqrt{s}=1.96\text{ }\text{ }\mathrm{TeV}$ by the D0 experiment at the Fermilab $p\overline{p}$ 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, ${\ensuremath{\sigma}}_{\mathrm{eff}}=2.2\ifmmode\pm\else\textpm\fi{}0.7(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.9(\mathrm{syst})\text{ }\text{ }\mathrm{mb}$.