Double parton scattering in $\overline{p}p$ collisions at $\sqrt{s}=1.8\mathrm{}\mathrm{TeV}$

A strong signal for double parton (DP) scattering is observed in a $16{\mathrm{pb}}^{\mathrm{-}1}$ sample of $\overline{p}p\to \gamma /{\pi }^0+3\mathrm{}\mathrm{jets}+X$ data from the CDF experiment at the Fermilab Tevatron. In DP events, two separate hard scatterings take place in a single $\overline{p}p$ collision. We isolate a large sample of data $\left(\sim 14000\mathrm{events}\right)$ of which 53% are found to be DP. The process-independent parameter of double parton scattering, ${\sigma }_{\mathrm{eff}},$ is obtained without reference to theoretical calculations by comparing observed DP events to events with hard scatterings in separate $\overline{p}p$ collisions. The result ${\sigma }_{\mathrm{eff}}=(14.5\mathrm{}\pm {1.7}_{-2.3}^{+1.7\mathrm{}})\mathrm{mb}$ represents a significant improvement over previous measurements, and is used to constrain simple models of parton spatial density. The Feynman $x$ dependence of ${\sigma }_{\mathrm{eff}}$ is investigated and none is apparent. Further, no evidence is found for kinematic correlations between the two scatterings in DP events.