Measurement of hard double-partonic interactions in $W \to l\nu$ + 2 jet events using the ATLAS detector at the LHC

The production of W bosons in association with two jets has been investigated using proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=7$ TeV. The fraction of $W+2$ jet events arising from double parton scattering was measured to be $f^{R}_{DP} = 0.16 \pm 0.01 (stat) \pm 0.03 (sys)$ for jets with transverse momentum $p_{T} \gt$ 20 GeV and rapidity |y|$\lt$ 2.8. This corresponds to an effective cross section for hard double partonic interactions of $\sigma_{eff} = 11 \pm 1$ (stat)$^{+3}_{-2}$ (sys) mb, which is consistent with previous measurements performed at lower centre-of-mass energies in different channels. This measurement was performed using data collected with the ATLAS detector corresponding to an integrated luminosity of 33$^{-1}$.