Abstract

The process pp → W^± J/ψ provides a powerful probe of the production mechanism of charmonium in hadronic collisions, and is also sensitive to multiple parton interactions. Using the 2011 ATLAS dataset of 4.5 fb⁻¹ of sqrt(s) = 7 TeV pp collisions, the first observation is made of the production of W^± + prompt J/ψ events in hadronic collisions, using W^± → μ ν_μ and J/ψ → μ⁺μ⁻. A yield of 27.4 +7.5 -6.5 W^± + prompt J/ψ events is observed, with a statistical significance of 5.1σ. The production ratio to inclusive W^± boson production is measured, and the double parton scattering contribution is estimated.