CERN Accelerating science

Article
Report number	arXiv:2306.03918 ; ANL-182798 ; DESY-23-068 ; FERMILAB-PUB-23-276-T ; MSUHEP-23-016 ; PITT-PACC-2315 ; SMU-HEP-23-02
Title	Quantifying the interplay of experimental constraints in analyses of parton distributions
Author(s)	Jing, Xiaoxian (Southern Methodist U.) ; Cooper-Sarkar, Amanda (Oxford U.) ; Courtoy, Aurore (Mexico U.) ; Cridge, Thomas (DESY) ; Giuli, Francesco (CERN) ; Harland-Lang, Lucian (University Coll. London) ; Hobbs, T.J. (Argonne) ; Huston, Joey (Michigan State U.) ; Nadolsky, Pavel (Southern Methodist U.) ; Thorne, Robert S. (University Coll. London) ; Xie, Keping (Pittsburgh U.) ; Yuan, C.-P. (Michigan State U.)
Publication	2023-08-01
Imprint	2023-06-06
Number of pages	57
Note	online plotter of L2 sensitivities for ATLASpdf21, CT18, MSHT20 PDFs at https://metapdf.hepforge.org/L2/
In:	Phys. Rev. D 108 (2023) 034029
DOI	10.1103/PhysRevD.108.034029 (publication)
Subject category	hep-ph ; Particle Physics - Phenomenology
Abstract	Parton distribution functions (PDFs) play a central role in calculations for the Large Hadron Collider (LHC). To gain a deeper understanding of the emergence and interplay of constraints on the PDFs in the global QCD analyses, it is important to examine the relative significance and mutual compatibility of the experimental data sets included in the PDF fits. Toward this goal, we discuss the L2 sensitivity, a convenient statistical indicator for exploring the statistical pulls of individual data sets on the best-fit PDFs and identifying tensions between competing data sets. Unlike the Lagrange Multiplier method, the L2 sensitivity can be quickly computed for a range of PDFs and momentum fractions using the published Hessian error sets. We employ the L2 sensitivity as a common metric to study the relative importance of data sets in the recent ATLAS, CTEQ-TEA, MSHT, and reduced PDF4LHC21 PDF analyses at NNLO and approximate N3LO. We illustrate how this method can aid the users of PDFs to identify data sets that are important for a PDF at a given kinematic point, to study quark flavor composition and other detailed features of the PDFs, and to compare the data pulls on the PDFs for various perturbative orders and functional forms. We also address the feasibility of computing the sensitivities using Monte Carlo error PDFs. Together with the article, we present a companion interactive website with a large collection of plotted L2 sensitivities for eight recent PDF releases.
Copyright/License	preprint: (License: arXiv nonexclusive-distrib 1.0) publication: © 2023-2025 authors (License: CC BY 4.0), sponsored by SCOAP³

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