  We use a sample of diphoton + dijet events to measure the effective cross
section of double parton interactions, which is found to be $\sigma_{\rm eff} =
19.3$ $\pm$ $1.4({\rm stat})$ $\pm$ $7.8({\rm syst})$ mb. The sample was
collected by the D0 detector at the Fermilab Tevatron collider in $p\bar{p}$
collisions at $\sqrt{s} = 1.96$ TeV and corresponds to an integrated luminosity
of 8.7 fb$^{-1}$.
