Measurement of hard double-parton interactions in $W (\rightarrow \ell \nu)$~+ 2 jet events at $\sqrt{s}=$~7~TeV with the ATLAS detector

The productions of jets in association with a vector boson are important processes for understanding the effect of QCD radiation on forward and central jet activity and can be used to study the contribution of multi-particle interactions. ATLAS results are compared with predictions from Monte Carlo simulations and next-to-leading order perturbative QCD predictions corrected for non-perturbative effects, which include multiple parton interactions and hadronisation effects. The contribution of double and multiple parton scattering plays a sizable contribution to vector bosons produced in association with light and heavy flavour jets, in the region of low jet transverse momentum. An explicit study of double-parton scattering using W+dijet events is presented, along with a measurement of the effective cross section.