The Impact of LHC Jet and $Z$ $p_T$ Data at up to Approximate N${}^3$LO Order in the MSHT Global PDF Fit

Abstract: We present an analysis of two key sets of data constraining the high $x$ gluon at up to approximate N${}^3$LO in QCD within the MSHT global PDF fitting framework. We begin with LHC 7 and 8 TeV inclusive jet and dijet production at both NNLO and aN${}^3$LO. This makes use of the formalism established in the previous global MSHT20aN${}^3$LO PDF fit, but now considers the role of dijet production for the first time at this order. We present a detailed comparison of the fit quality and PDF impact for both cases, and consider the role that electroweak corrections, and the scale choice for inclusive jet production has. Some mild tension between these data sets in the impact on the high $x$ gluon is seen at NNLO, but this is largely eliminated at aN${}^3$LO. While a good fit quality to the dijet data is achieved at both orders, the fit quality to the inclusive jet data is relatively poor. We examine the impact of including full colour corrections in a global PDF fit for the first time, finding this to be relatively mild. We also revisit the fit to the ATLAS 8 TeV $Z$ $p_T$ data, considering the role that the $p_T$ cuts, data selection and different aspects of the aN${}^3$LO treatment have on the fit quality and PDF impact. We observe that in all cases the aN${}^3$LO fit quality is consistently improved relative to the NNLO, indicating a clear preference for higher order theory for these data.