W+J/ψ Associated Production with ATLAS

The process pp→W J/ψ X provides a powerful probe of the production mechanism of charmonium in hadronic collisions, and is also sensitive to multiple parton interactions in the colliding protons. Using the 2011 ATLAS dataset of 4.6 fb-1 of pp collisions at √s= 7 TeV, the first observation is made of the production of W±+ prompt J/ψ events in hadronic collisions where the W± boson and the J/ψ both decay to muons. A total of 29.2+7.5-6.5 W± + prompt J/ψ events is observed, with a statistical significance of 5.3σ. The production rate as a ratio to the inclusive W± boson production rate is measured, and the double parton scattering contribution to the cross section is estimated. Comparisons to predictions from Color Singlet and Color Octet models are also shown.