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arxiv: 1907.08147 · v1 · pith:F5ABEYC7new · submitted 2019-07-18 · ✦ hep-ph · hep-ex

Updates of PDFs in the MMHT framework

R.S. Thorne , S. Bailey , T. Cridge , L.A. Harland-Lang , A.D. Martin , R. Nathvani This is my paper

Pith reviewed 2026-05-24 19:43 UTC · model grok-4.3

classification ✦ hep-ph hep-ex
keywords parton distribution functionsstrange quarkNNLO QCDcharged current processesglobal PDF fits
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The pith

Improved NNLO calculations for charged current cross sections refine the strange quark distribution in the MMHT PDFs.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper summarises updates toward the MMHT19 set of parton distribution functions. The central focus is the improved extraction of the strange quark PDF, which results from more accurate next-to-next-to-leading-order theoretical predictions for charged current processes, an extended form of the PDF parameterisation, and explicit handling of correlated uncertainties in data sets that have been hard to accommodate. A reader would care because the strange quark PDF has been one of the less well-constrained components in global fits, and its better determination directly affects the precision of predictions for many LHC processes that involve strange quarks.

Core claim

The extraction of the strange quark is improved upon the improvement of theoretical calculations for NNLO charged current cross sections, an extension of the parameterisation, and the role of correlated uncertainties in some data sets which prove difficult to fit.

What carries the argument

NNLO theoretical calculations for charged current cross sections together with an extended PDF parameterisation for the strange quark.

If this is right

  • The updated strange quark PDF yields narrower uncertainty bands for processes such as W and Z production at the LHC.
  • The extended parameterisation allows the strange distribution to differ more flexibly from the down-quark distribution at low x.
  • Accounting for correlated uncertainties in previously problematic data sets produces a more consistent global fit.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same combination of improved theory and flexible parameterisation could be applied to other sea-quark flavours in future fits.
  • If the NNLO charged-current calculations prove stable under further higher-order corrections, the method sets a template for reducing PDF uncertainties in other channels.
  • The emphasis on correlated systematics suggests that re-examination of older neutrino data sets with modern uncertainty treatments may further tighten the strange PDF.

Load-bearing premise

The improved NNLO theoretical calculations for charged current cross sections are accurate enough and free of significant higher-order or non-perturbative effects that would invalidate the strange quark extraction when fitted to data.

What would settle it

A new high-precision measurement of a strange-quark-sensitive observable, such as a charged-current dimuon production cross section at the LHC, that lies well outside the uncertainty band of the updated MMHT19 strange PDF would falsify the improvement claim.

Figures

Figures reproduced from arXiv: 1907.08147 by A.D. Martin, L.A. Harland-Lang, R. Nathvani, R.S. Thorne, S. Bailey, T. Cridge.

Figure 1
Figure 1. Figure 1: The strange over the light quark average and change in strange on addition of ATLAS W,Z data without full NNLO as in MMHT2014 (top), and with full NNLO and the updated VFNS (bottom). With the inclusion of more constraining LHC data we examine the introduction of more free parameters in our functions for the input PDFs. In [8] we changed our previous parameterisation to one with most PDFs parameterised as A… view at source ↗
Figure 2
Figure 2. Figure 2: The NNLO down valence (left) and d¯−u¯ (right) for the fits with extended parameterisation [PITH_FULL_IMAGE:figures/full_fig_p005_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: The NNLO gluon (left) and ¯u (right) for the fits with extended parameterisation. As well as these main results on the way to presenting the new updated “MMHT2019” PDFs, we note some other recent developments. In a previous study [10] we found difficulty in fitting ATLAS 7 TeV inclusive jet data [11], even with full NNLO [12]. To alleviate this we investigated decorrelation of some systematic uncertainties… view at source ↗
read the original abstract

We summarise recent developments in the path towards the "MMHT19" parton distribution functions. We concentrate on the extraction of the strange quark upon the improvement of theoretical calculations for NNLO charged current cross sections; the effect of an extension of our parameterisation; and the role of correlated uncertainties in some data sets which prove difficult to fit.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

0 major / 2 minor

Summary. The manuscript summarises recent developments towards the MMHT19 parton distribution functions, concentrating on the extraction of the strange quark. The claimed improvements arise from three updates: refined NNLO theoretical calculations for charged-current cross sections, an extension of the PDF parameterisation, and improved treatment of correlated uncertainties in data sets that are difficult to fit.

Significance. If substantiated by the underlying fits, these incremental advances would contribute to more reliable strange-quark distributions, which enter precision predictions for W/Z production and heavy-flavour processes at the LHC. The explicit focus on concrete methodological steps (theory calculations, parameterisation, and uncertainty treatment) is a positive feature of the work.

minor comments (2)
  1. The manuscript is presented as a summary; inclusion of at least one quantitative illustration (e.g., change in the strange-quark uncertainty band or χ² improvement) would strengthen the central claim without requiring a full technical appendix.
  2. [Abstract] A brief statement on the status of the full MMHT19 release (or a reference to the companion paper) would help readers locate the complete fit results and tables.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for the positive assessment of our manuscript on updates to the MMHT PDFs, with emphasis on the strange quark extraction, and for recommending minor revision. No specific major comments were provided in the report.

Circularity Check

0 steps flagged

No significant circularity in methodological PDF updates

full rationale

The paper summarises incremental updates to the MMHT global PDF fit procedure, specifically improved NNLO charged-current cross-section calculations, an extended parameterisation, and handling of correlated uncertainties for strange-quark extraction. These steps rely on external experimental data sets and independent theoretical computations rather than any self-referential derivation, fitted input renamed as prediction, or load-bearing self-citation chain. No equations or claims in the provided text reduce the outputs to the inputs by construction; the work is a standard empirical update validated against data.

Axiom & Free-Parameter Ledger

2 free parameters · 1 axioms · 0 invented entities

Only the abstract is available, so the ledger is necessarily incomplete. PDF fits of this type rest on many fitted parameters for quark and gluon distributions plus standard QCD assumptions.

free parameters (2)
  • strange quark distribution parameters
    The strange quark PDF is extracted by fitting to data; its functional form and coefficients are free parameters adjusted to match measurements.
  • extended parameterization coefficients
    An extension of the parameterization introduces additional free parameters whose values are determined by the fit.
axioms (1)
  • domain assumption QCD factorization and perturbative calculations at NNLO are valid for the charged current processes used.
    Invoked when stating that improved NNLO calculations allow better strange quark extraction.

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Forward citations

Cited by 1 Pith paper

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