  Because of its forward coverage, LHCb can probe the valence quark
distributions of protons and nuclei at small and large Bjorken-x with high
precision. This proceeding presents new LHCb measurements of Z boson production
in association with charm jet in the forward region of proton-proton collisions
and Z boson production in proton-lead collisions. Z+charm jet production could
be sensitive to a valence-like intrinsic-charm component in the proton wave
function. The measurements of Z production in proton-lead collisions provide
new constraints on the partonic structure of nucleons inside nuclei.
Comparisons between the results and calculations with parton distribution
functions are also discussed.
