Measurement of the the production of a $W$ boson in association with charm quark at $\sqrt{s}=13$ TeV with ATLAS detector.

One of the major challenges for the proton-proton collider physics is to increase the precision of proton parton distribution functions (pdfs). Actually, most of the physics results delivered by LHC experiments are affected by their uncertainties. While the valence quark pdfs are known with relatively good precision, the uncertainty on the strange pdf is considerably larger. In this contribution, I will show an ATLAS analysis that aims to constrain the strange pdf through the study of the associated production of $W$ boson with charm quark (tagged as a jet containing a soft muon).