Measurement of hard double-parton interactions with the ATLAS detector

The production of a W boson in association with two jets was studied in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 7$ TeV with the ATLAS detector. Data corresponding to an integrated luminosity of 36 pb$^{-1}$ were analysed for the presence of double-parton interactions. The fraction of events arising from double-parton interactions was extracted using the momentum balance of the two jets and was evaluated to be $f_{\rm DP}^{\rm Detector} = 0.08 \pm 0.01 ({\rm stat.}) \pm 0.02 ({\rm syst.})$ for jets with transverse momentum $p_{\rm T} > 20 $ GeV and rapidity $|y| < 2$. This is expressed as a measure of the effective area parameter for hard double-parton interactions, $\sigma_{\rm eff} = 15 \pm 3 ({\rm stat.}) ^{+5}_{-3} ({\rm syst.})$ mb.