“…Due to the challenge of reducing their uncertainties and empirically distinguishing among their parton flavors, PDFs have historically been determined most robustly through "global QCD fits" [5][6][7][8], now increasingly performed at nextto-next-to-leading order (NNLO) accuracy in α s , and drawing upon large collections of experimental measurements sensitive to QCD and different underlying PDF combinations. In spite of the growing number of LHC measurements, deeply-inelastic scattering (DIS) experiments involving fixed hadronic or nuclear targets at BCDMS, NMC, SLAC, and JLab continue to provide key information to disentangle the PDFs in recent global QCD analyses such as CJ15 [9], ABMP16 [10], CT18 [11], NNPDF3.1 [12], and MSHT20 [13]. The fixed-target experiments complement analogous DIS collisions at the HERA ep collider by extending the momentum fraction coverage to larger x values and adding measurements on deuterium targets.…”