Journal Article

PUBDB-2025-04238

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png A stress test of global PDF fits: closure testing the MSHT PDFs and a first direct comparison to the neural net approach

Harland-Lang, L. A. (Corresponding author) ; Cridge, T.Extern*DESY* ; Thorne, R. S.

2025
Springer Heidelberg

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Please use a persistent id in citations: doi:10.1140/epjc/s10052-025-13934-3  doi:10.3204/PUBDB-2025-04238

Report No.: DESY-24-101; arXiv:2407.07944

Abstract: We present a first global closure test of the fixed parameterisation (MSHT) approach to PDF fitting. We find that the default MSHT20 parameterisation can reproduce the features of the input set in such a closure test to well within the textbook uncertainties. This provides strong evidence that parameterisation inflexibility in the MSHT20 fit is not a significant issue in the data region. We also present the first completely like-for-like comparison between two global PDF fits, namely MSHT and NNPDF, where the only difference is guaranteed to be due to the fitting methodology. To achieve this, we present a fit to the NNPDF4.0 data and theory inputs, but with the MSHT fixed parameterisation. We find that this gives a moderately, but noticeably, better fit quality than the central NNPDF4.0 fits, both with perturbative and fitted charm, and that this difference persists at the level of the PDFs and benchmark cross sections. The NNPDF4.0 uncertainties are found to be broadly in line with the MSHT results if a textbook $T^2=1$ tolerance is applied, but to be significantly smaller if a tolerance typical of the MSHT20 fit is applied. This points to an inherent inconsistency between these approaches. We discuss the need for an enlarged tolerance criterion in global PDF fits in detail, and demonstrate the impact of data/theory inconsistencies in the closure test setting; namely, these do not lead to any increase in the $T^2=1$ PDF uncertainty. We also investigate the impact of restricting the PDF parameterisation to have fewer free parameters than the default MSHT20 case, and find this can be significant at the level of both closure tests and the full fit.

Note: Creative Commons Attribution 4.0 International License

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Contributing Institute(s):

1. Theorie-Gruppe (T)

Research Program(s):

1. 611 - Fundamental Particles and Forces (POF4-611) (POF4-611)
2. COLORFREE - High-Precision Global Analysis of Color-Free LHC Processes at Small Recoil (101002090) (101002090)

Experiment(s):

1. No specific instrument

Appears in the scientific report 2025

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Database coverage:
; ; ; ; ; Clarivate Analytics Master Journal List ; Current Contents - Physical, Chemical and Earth Sciences ; DOAJ Seal ; Ebsco Academic Search ; Essential Science Indicators ; IF < 5 ; JCR ; SCOAP3 sponsored Journal ; SCOPUS ; Science Citation Index Expanded ; Web of Science Core Collection

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Linked articles:

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Preprint Harland-Lang, L. A. (Corresponding author) ; Cridge, T.DESY* ; Thorne, R. S.
A Stress Test of Global PDF Fits: Closure Testing the MSHT PDFs and a First Direct Comparison to the Neural Net Approach
[10.3204/PUBDB-2024-05022]     Files  Fulltext by arXiv.org BibTeX | EndNote: XML, Text | RIS

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