Double parton interactions in γ = 3 jet events in pp collisions at √s= 1.96 TeV

We have used a sample of γ + 3 jets events collected by the D0 experiment with an integrated luminosity of about 1 fb -1 to determine the fraction of events with double parton scattering (f DP ) in a single pp collision at √s = 1.96 TeV. The DP fraction and effective cross section (σ 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 jet2 T within the range 15 ≤ p jet2 T ≤ 30 GeV. In this range, f DP varies between 0.23 ≤ f DP ≤ 0.47, while σ eff has the average value σ ave eff = 16.4 ± 0.3(stat) ± 2.3(syst) mb.