A reassessment of the role of high $x$ data on the MSHT global PDF fit

Abstract: We present updates within the MSHT global PDF fit that focus on the high $x$ region, and on improving our understanding of the interplay of various theoretical contributions and experimental constraints here. We revisit the question of target mass and higher twist corrections, considering their impact for the first time at approximate N$^3$LO order in a global PDF analysis. Their inclusion is found to be moderate but not negligible on both the PDFs and preferred value of the strong coupling. Increased stability in these at aN$^3$LO is observed in comparison to lower orders. We also study the impact of an updated treatment of various fixed-target DIS data, the inclusion of Seaquest fixed-target Drell Yan data, and new ZEUS data that extends coverage into the high $x$ region. The Seaquest data have the largest effect of these, in particular on the light quark separation at high $x$, while the impact of the other updates is rather mild.