We have used a sample of $\gamma +3$ jets events collected by the D0 experiment with an integrated luminosity of about $1{\mathrm{fb}}^{-1}$ to determine the fraction of events with double parton scattering ($f_{\mathrm{DP}}$) in a single $p\overline{p}$ collision at $\sqrt{s}=1.96\mathrm{TeV}$. The DP fraction and effective cross section (${\sigma }_{\mathrm{eff}}$), a process-independent scale parameter related to the parton density inside the nucleon, are measured in three intervals of the second (ordered in $p_T$) jet transverse momentum $p_T^{\mathrm{jet}2}$ within the range $15\le p_T^{\mathrm{jet}2}\le 30\mathrm{GeV}$. In this range, $f_{\mathrm{DP}}$ varies between $0.23\le f_{\mathrm{DP}}\le 0.47$, while ${\sigma }_{\mathrm{eff}}$ has the average value ${\sigma }_{\mathrm{eff}}^{\mathrm{ave}}=16.4\pm 0.3(\mathrm{stat})\pm 2.3(\mathrm{syst})\mathrm{mb}$.

• Received 27 December 2009

DOI:https://doi.org/10.1103/PhysRevD.81.052012