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Impact of the heavy quark matching scales in PDF fits | | xFitter Developers Team
; V. Bertone
; D. Britzger
; S. Camarda
; A. Cooper-Sarkar
; A. Geiser
; F. Giuli
; A. Glazov
; E. Godat
; A. Kusina
; A. Luszczak
; F. Lyonnet
; F. Olness
; R. Placakyte
; V. Radescu
; I. Schienbein
; O. Zenaiev
; | | Date: |
17 Jul 2017 | | Abstract: | We investigate the impact of displaced heavy quark matching scales in a
global fit. The heavy quark matching scale $mu_{m}$ determines at which energy
scale $mu$ the QCD theory transitions from $N_{F}$ to $N_{F}+1$ in the
Variable Flavor Number Scheme (VFNS) for the evolution of the Parton
Distribution Functions (PDFs) and strong coupling $alpha_S(mu)$. 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 $mu_{m}$ 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 $N_{F}=3$ to $4$), we find a large $mu_m=mu_{c}$
dependence of the global fit $chi^2$ at NLO, but this is significantly reduced
at NNLO. For the transition across the bottom quark (from $N_{F}=4$ to $5$), we
have a reduced $mu_{m}=mu_b$ dependence of the $chi^2$ at both NLO and NNLO;
as this transition falls in the region of many high precision data sets used in
the global fits (especially the HERA data), this will yield a reduced
theoretical uncertainty. This feature is now implemented in xFitter 2.0.0, an
open source QCD fit framework. | | Source: | arXiv, 1707.5343 | | Services: | Forum | Review | PDF | Favorites | |
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