Measurement of Double Parton Scattering inp¯pCollisions ats}=1.8TeV

A strong signal for double parton scattering (DP) is observed in a $16\mathrm{pb}{}^{-1\mathrm{}}$ sample of $\overline{p}p\to \gamma +3\mathrm{}\mathrm{jets}+X$ data from the CDF experiment at the Fermilab Tevatron. The process-independent DP parameter, ${\sigma }_{\mathrm{eff}}$, is obtained without reference to theoretical calculations by comparing observed DP events to events with hard scatterings at separate $\overline{p}p$ collisions. The result, ${\sigma }_{\mathrm{eff}}=(14.5\pm {1.7}_{-2.3\mathrm{}}^{+1.7\mathrm{}})\mathrm{mb}$, represents a significant improvement over previous measurements. For the first time, the Feynman $x$ dependence of the ${\sigma }_{\mathrm{eff}}$ parameter is investigated, and no dependence is seen.