Direct Measurement of DPS at ATLAS

The production of W bosons in association with two jets in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV has been investigated using data corresponding to an integrated luminosity of 36 pb-1, collected with the ATLAS detector. The fraction of events arising from double-parton scattering, fDP , has been measured through the pT balance between the two jets and amounts to fDP = 0.08+-0.01(stat)+-0.02(sys) for jets with transverse momentum pT > 20 GeV and rapidity |y| < 2.8. This translates into an effective cross section for hard double-parton interactions of sigma_eff = 15+-3(stat)+5-3(sys) mb.