Impact of the heavy-quark matching scales in PDF fits

; Bertone, V. (Department of Physics and Astronomy, VU University, 0000 0004 1754 9227, 1081 HV, Amsterdam, The Netherlands) (Nikhef Theory Group Science Park 105, 0000 0004 0646 2193, 1098 XG, Amsterdam, The Netherlands) ; Britzger, D. (DESY Hamburg, 0000 0004 0492 0453, Notkestraße 85, 22609, Hamburg, Germany) ; Camarda, S. (CERN, 0000 0001 2156 142X, 1211, Geneva 23, Switzerland) ; Cooper-Sarkar, A. (University of Oxford, 0000 0004 1936 8948, 1 Keble Road, OX1 3NP, Oxford, UK) ; Geiser, A. (DESY Hamburg, 0000 0004 0492 0453, Notkestraße 85, 22609, Hamburg, Germany) ; Giuli, F. (University of Oxford, 0000 0004 1936 8948, 1 Keble Road, OX1 3NP, Oxford, UK) ; Glazov, A. (DESY Hamburg, 0000 0004 0492 0453, Notkestraße 85, 22609, Hamburg, Germany) ; Godat, E. (SMU Physics, 0000 0004 1936 7929, Box 0175, 75275-0175, Dallas, TX, USA) ; Kusina, A. (Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble Alpes, CNRS/IN2P3, 53 avenue des Martyrs, 38026, Grenoble, France) (Institute of Nuclear Physics, Polish Academy of Sciences, 0000 0001 1958 0162, ul. Radzikowskiego 152, 31-342, Kraków, Poland) ; Luszczak, A. (T.Kosciuszko Cracow University of Technology, 0000000100375134, 30-084, Kraków, Poland) ; Lyonnet, F. (SMU Physics, 0000 0004 1936 7929, Box 0175, 75275-0175, Dallas, TX, USA) ; Olness, F. (SMU Physics, 0000 0004 1936 7929, Box 0175, 75275-0175, Dallas, TX, USA) ; Plačakytė, R. (Institut für Theoretische Physik, Universität Hamburg, 0000 0001 2287 2617, Luruper Chaussee 149, 22761, Hamburg, Germany) ; Radescu, V. (DESY Hamburg, 0000 0004 0492 0453, Notkestraße 85, 22609, Hamburg, Germany) (CERN, 0000 0001 2156 142X, 1211, Geneva 23, Switzerland) ; Schienbein, I. (Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble Alpes, CNRS/IN2P3, 53 avenue des Martyrs, 38026, Grenoble, France) ; Zenaiev, O. (DESY Hamburg, 0000 0004 0492 0453, Notkestraße 85, 22609, Hamburg, Germany)

07 December 2017

Abstract: We investigate the impact of displaced heavy-quark matching scales in a global fit. The heavy-quark matching scale μm determines at which energy scale μ the QCD theory transitions from NF to NF+1 in the variable flavor number scheme (VFNS) for the evolution of the parton distribution functions (PDFs) and strong coupling αS(μ) . We study the variation of the matching scales, and their impact on a global PDF fit of the combined HERA data. As the choice of the matching scale μm effectively is a choice of scheme, this represents a theoretical uncertainty; ideally, we would like to see minimal dependence on this parameter. For the transition across the charm quark (from NF=3 to 4), we find a large μm=μc dependence of the global fit χ2 at NLO, but this is significantly reduced at NNLO. For the transition across the bottom quark (from NF=4 to 5), we have a reduced μm=μb dependence of the χ2 at both NLO and NNLO as compared to the charm. This feature is now implemented in xFitter 2.0.0, an open source QCD fit framework.


Published in: EPJC 77 (2017) 837
Published by: Springer/Società Italiana di Fisica
DOI: 10.1140/epjc/s10052-017-5407-3
License: CC-BY-3.0



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