First measurement of the associated production of $W^{\pm}$ bosons and prompt $J/\Psi$ mesons at the ATLAS experiment

The first observation of the production of a prompt $J/\Psi$ meson in association with a $W^{\pm}$ boson in a dataset collected in the year 2011 by the ATLAS detector in $\sqrt{s}= 7$ TeV $pp$ collisions at the LHC, corresponding to 4.5 fb$^{-1}$, using the $W^{\pm}\to\mu^{\pm}\nu$ and $J/\Psi\to\mu^{+}\mu^{-}$ decay modes, is reported. The $W^{\pm}$+ prompt $J/\Psi$ cross section is measured relative to the inclusive $W^{\pm}$ cross section. The results are compared to theoretical predictions to probe different mechanisms of charmonium production in hadronic collisions.