We report evidence for the simultaneous production of J/ψ and ϒ mesons in 8.1 fb−1 of data collected at [?] = 1.96 TeV by the D0 experiment at the Fermilab pp 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, σeff = 2.2 ± 0.7(stat) ± 0.9(syst) mb
