Associated production of $J/\psi$ and $W$ in ATLAS

We present the discovery of associated vector boson+prompt $J/\psi$ production and subsequent measurement of the production rate, which is a key observable to furthering understanding of quarkonium production mechanisms. We estimate the relative contributions to the signal from single and double parton scattering and discuss possible implications of this novel final state for study of multiple parton interactions. The single parton scattering cross-sections are compared to cutting-edge theoretical calculations in the colour singlet and colour octet formalisms.