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      Regularising experimental correlations in LHC data: theory and application to a global analysis of parton distributions

      Author(s): , ,
      Publication date Created:
      Publication date (Electronic):
      Journal: The European Physical Journal C
      Publisher: Springer Science and Business Media LLC

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          Abstract

          We show how an inaccurate determination of experimental uncertainty correlations in high-precision LHC measurements may undermine the reliability of the associated \[\chi ^2\] . We formulate the problem rigorously, and devise a regularisation procedure that increases the stability of the \[\chi ^2\] by altering the covariance matrix of the measurement as little as possible. We apply the procedure to the NNPDF4.0 global analysis of parton distribution functions that utilises a large amount of LHC measurements. We find that the regularised \[\chi ^2\] of the NNPDF4.0 determination is lowered by about \[3\sigma \] , without significantly altering the resulting PDFs upon refitting.

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          LHAPDF6: parton density access in the LHC precision era

          Andy Buckley, James Ferrando, Stephen Lloyd … (2015)
          Article 0 comments Cited 156 times – based on 0 reviews     Review now
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            Parton distributions from high-precision collider data

            Richard Ball, Valerio Bertone, Stefano Carrazza … (2017)
            We present a new set of parton distributions, NNPDF3.1, which updates NNPDF3.0, the first global set of PDFs determined using a methodology validated by a closure test. The update is motivated by recent progress in methodology and available data, and involves both. On the methodological side, we now parametrize and determine the charm PDF alongside the light-quark and gluon ones, thereby increasing from seven to eight the number of independent PDFs. On the data side, we now include the D0 electron and muon W asymmetries from the final Tevatron dataset, the complete LHCb measurements of W and Z production in the forward region at 7 and 8 TeV, and new ATLAS and CMS measurements of inclusive jet and electroweak boson production. We also include for the first time top-quark pair differential distributions and the transverse momentum of the Z bosons from ATLAS and CMS. We investigate the impact of parametrizing charm and provide evidence that the accuracy and stability of the PDFs are thereby improved. We study the impact of the new data by producing a variety of determinations based on reduced datasets. We find that both improvements have a significant impact on the PDFs, with some substantial reductions in uncertainties, but with the new PDFs generally in agreement with the previous set at the one-sigma level. The most significant changes are seen in the light-quark flavor separation, and in increased precision in the determination of the gluon. We explore the implications of NNPDF3.1 for LHC phenomenology at Run II, compare with recent LHC measurements at 13 TeV, provide updated predictions for Higgs production cross-sections and discuss the strangeness and charm content of the proton in light of our improved dataset and methodology. The NNPDF3.1 PDFs are delivered for the first time both as Hessian sets, and as optimized Monte Carlo sets with a compressed number of replicas.
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              Parton distributions in the LHC era: MMHT 2014 PDFs

              L. Harland-Lang, A Martin, P. Motylinski … (2015)
              We present LO, NLO and NNLO sets of parton distribution functions (PDFs) of the proton determined from global analyses of the available hard scattering data. These MMHT2014 PDFs supersede the ‘MSTW2008’ parton sets, but they are obtained within the same basic framework. We include a variety of new data sets, from the LHC, updated Tevatron data and the HERA combined H1 and ZEUS data on the total and charm structure functions. We also improve the theoretical framework of the previous analysis. These new PDFs are compared to the ‘MSTW2008’ parton sets. In most cases the PDFs, and the predictions, are within one standard deviation of those of MSTW2008. The major changes are the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$u-d$$\end{document} u - d valence quark difference at small \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$x$$\end{document} x due to an improved parameterisation and, to a lesser extent, the strange quark PDF due to the effect of certain LHC data and a better treatment of the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$D \rightarrow \mu $$\end{document} D → μ branching ratio. We compare our MMHT PDF sets with those of other collaborations; in particular with the NNPDF3.0 sets, which are contemporary with the present analysis.
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                Author and article information

                Contributors
                Emanuele R. Nocera: (View ORCID Profile)
                Journal
                Title: The European Physical Journal C
                Abbreviated Title: Eur. Phys. J. C
                Publisher: Springer Science and Business Media LLC
                ISSN (Electronic): 1434-6052
                Publication date Created: October 2022
                Publication date (Electronic): October 27 2022
                Volume: 82
                Issue: 10
                Article
                DOI: 10.1140/epjc/s10052-022-10932-7
                SO-VID: 2643fa08-025a-480e-8bb9-351e2c43e2ad
                Copyright © © 2022
                License:

                https://creativecommons.org/licenses/by/4.0

                https://creativecommons.org/licenses/by/4.0

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