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An investigation of the $$\alpha _S$$ and heavy quark mass dependence in the MSHT20 global PDF analysis

Cridge, T.; Harland-Lang, L.A.; Martin, A.D.; Thorne, R.S.

An investigation of the $$\alpha _S$$ and heavy quark mass dependence in the MSHT20 global PDF analysis Thumbnail


T. Cridge

L.A. Harland-Lang

A.D. Martin

R.S. Thorne


We investigate the MSHT20 global PDF sets, demonstrating the effects of varying the strong coupling αS(M2Z) and the masses of the charm and bottom quarks. We determine the preferred value, and accompanying uncertainties, when we allow αS(M2Z) to be a free parameter in the MSHT20 global analyses of deep-inelastic and related hard scattering data, at both NLO and NNLO in QCD perturbation theory. We also study the constraints on αS(M2Z) which come from the individual data sets in the global fit by repeating the NNLO and NLO global analyses at various fixed values of αS(M2Z), spanning the range αS(M2Z)=0.108 to 0.130 in units of 0.001. We make all resulting PDFs sets available. We find that the best fit values are αS(M2Z)=0.1203±0.0015 and 0.1174±0.0013 at NLO and NNLO respectively. We investigate the relationship between the variations in αS(M2Z) and the uncertainties on the PDFs, and illustrate this by calculating the cross sections for key processes at the LHC. We also perform fits where we allow the heavy quark masses mc and mb to vary away from their default values and make PDF sets available in steps of Δmc=0.05 GeV and Δmb=0.25 GeV, using the pole mass definition of the quark masses. As for varying αS(M2Z) values, we present the variation in the PDFs and in the predictions. We examine the comparison to data, particularly the HERA data on charm and bottom cross sections and note that our default values are very largely compatible with best fits to data. We provide PDF sets with 3 and 4 active quark flavours, as well as the standard value of 5 flavours.


Cridge, T., Harland-Lang, L., Martin, A., & Thorne, R. (2021). An investigation of the $$\alpha _S$$ and heavy quark mass dependence in the MSHT20 global PDF analysis. The European Physical Journal C, 81(8), Article 744.

Journal Article Type Article
Acceptance Date Aug 6, 2021
Online Publication Date Aug 17, 2021
Publication Date 2021-08
Deposit Date Jan 19, 2022
Publicly Available Date Jan 20, 2022
Journal The European Physical Journal C
Print ISSN 1434-6044
Electronic ISSN 1434-6052
Publisher SpringerOpen
Peer Reviewed Peer Reviewed
Volume 81
Issue 8
Article Number 744


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