W and Z bosons are produced at the LHC when a quark and anti-quark contained in each of the colliding protons fuse together. Due to the quantum mechanical nature of the strong force, which quarks and anti-quarks you see depends on how you collide the protons. The structure of the proton is described by the parton distribution functions (pdf). The plot shows the uncertainty in 2010 on the W and Z ratio and asymmetry due to knowledge of the pdfs (y-axis) as a function of how forward the collision is (x-axis). LHCb is instumented between 2 and 5 so in fact our measurements made the largest improvements in understanding the pdfs. We developed a method for showing by how much a measurement would improve the pdfs and it is described in Francesco's thesis.

(One of the main goals of the new EIC collider, due to start in the 2030s, is to determine the pdfs precisely. To understand pdfs better, view this video.)