Impact of the heavy-quark matching scales in PDF fits

Bertone, V.; Kusina, A.; Luszczak, A.; Cooper-Sarkar, A.; Glazov, A.; Britzger, D.; Olness, F.; Camarda, S.; Lyonnet, F.; Radescu, V.; Plačakytė, R.; Giuli, F.; Schienbein, I.; Godat, E.; Geiser, A.; Zenaiev, O.

doi:10.1140/epjc/s10052-017-5407-3

Report/Journal Article

PUBDB-2018-00530

Impact of the heavy-quark matching scales in PDF fits

Bertone, V. ; Britzger, D.DESY* ; Camarda, S. ; Cooper-Sarkar, A. ; Geiser, A.DESY* ; Giuli, F. ; Glazov, A. (Corresponding author)DESY* ; Godat, E. ; Kusina, A. ; Luszczak, A.DESY* ; Lyonnet, F. ; Olness, F. (Corresponding author) ; Plačakytė, R.Extern* ; Radescu, V.Extern* ; Schienbein, I. ; Zenaiev, O.DESY*

2017
Springer Berlin

The European physical journal / C 77(12), 837 (2017) [10.1140/epjc/s10052-017-5407-3]

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Please use a persistent id in citations: doi:10.1140/epjc/s10052-017-5407-3 doi:10.3204/PUBDB-2018-00530

Report No.: DESY-17-101; arXiv:1707.05343

Abstract: We investigate the impact of displaced heavy-quark matching scales in a global fit. The heavy-quark matching scale $μ_m$ determines at which energy scale $μ$ the QCD theory transitions from NF to $N_{F}+1$ in the variable flavor number scheme (VFNS) for the evolution of the parton distribution functions (PDFs) and strong coupling $\alpha_{S}(μ)$. 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 $μ_m$ 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 $μ_m = μ_c$ dependence of the global fit $χ^2$ 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$μ_m = μ_b$ dependence of the $χ^2$ 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.

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