  This article presents a new set of proton parton distribution functions,
ATLASepWZVjet20, produced in an analysis at next-to-next-to-leading order in
QCD. The new data sets considered are the measurements of $W^+$ and $W^-$ boson
and $Z$ boson production in association with jets in $pp$ collisions at
$\sqrt{s} = 8~\mathrm{TeV}$ performed by the ATLAS experiment at the LHC with
integrated luminosities of $20.2~\mathrm{fb}^{-1}$ and $19.9~\mathrm{fb}^{-1}$,
respectively. The analysis also considers the ATLAS measurements of
differential $W^{\pm}$ and $Z$ boson production at $\sqrt{s} = 7~\mathrm{TeV}$
with an integrated luminosity of $4.6~\mathrm{fb}^{-1}$ and
deep-inelastic-scattering data from $e^{\pm}p$ collisions at the HERA
accelerator. An improved determination of the sea-quark densities at high
Bjorken $x$ is shown, while confirming a strange-quark density similar in size
to the up- and down-sea-quark densities in the range $x \lesssim 0.02$ found by
previous ATLAS analyses.
