Uncertainties on αS in the MMHT2014 global PDF analysis and implications for SM predictions

We investigate the uncertainty in the strong coupling alpha(S)(M-Z(2)) when allowing it to be a free parameter in the recent MMHT global analyses of deep-inelastic and related hard scattering data that was undertaken to determine the parton distribution functions (PDFs) of the proton. The analysis uses the standard framework of leading twist fixed-order collinear factorisation in the (MS) over bar scheme. We study the constraints on alpha(S)(M-Z(2)) coming from individual data sets by repeating the NNLO and NLO fits spanning the range 0.108 to 0.128 in units of 0.001, making all PDFs sets available. The inclusion of the cross section for inclusive t (t) over bar production allows us to explore the correlation between the mass m(t) of the top quark and alpha(S)(M-Z(2)). We find that the best-fit values are alpha(S)(M-Z(2)) = 0.1201 +/- 0.0015 and 0.1172 +/- 0.0013 at NLO and NNLO, respectively, with the central values changing to alpha(S)(M-Z(2)) = 0.1195 and 0.1178 when the world average of alpha(S)(M-Z(2)) is used as a data point. We investigate the interplay between the uncertainties on alpha(S)(M-Z(2)) and on the PDFs. In particular we calculate the cross sections for key processes at the LHC and show how the uncertainties from the PDFs and from alpha(S)(M-Z(2)) can be provided independently and be combined.