NLO PDFs from the ABMP16 fit

Abstract

We perform a global fit of parton distribution functions (PDFs) together with the strong coupling constant $α_s$ and the quark masses $m_c$, $m_b$ and $m_t$ at next-to-leading order (NLO) in QCD. The analysis applies the $\overline{\mathrm{MS}}\, $ renormalization scheme for $α_s$ and all quark masses. It is performed in the fixed-flavor number scheme for $n_f=3, 4, 5$ and uses the same data as the previous fit of the ABMP16 PDF at next-to-next-to-leading order (NNLO). The new NLO PDFs complement the set of ABMP16 PDFs and are to be used consistently with NLO QCD predictions for hard scattering processes. At NLO we obtain the value $α_s^{(n_f=5)}(M_Z) = 0.1191 \pm 0.0011$ compared to $α_s^{(n_f=5)}(M_Z) = 0.1147 \pm 0.0008$ at NNLO.

Figures (4)

• Figure 1: The $1\sigma$ band for the $n_f=3$ flavor NNLO ABM16 PDFs Alekhin:2017kpj for a) gluon, b) up-quarks c) down-quarks d) the symmetrized strange sea and e) the non-strange sea, at the scale of $\mu = 3$ GeV versus $x$ (shaded area) compared with the relative difference of those PDFs to the NLO ABMP16 ones obtained in the present analysis (solid lines). The dotted lines display $1\sigma$ band for the NLO PDFs.
• Figure 2: The relative difference between $\alpha_s^{\rm NLO}(\mu)$ and $\alpha_s^{\rm NNLO}(\mu)$ as a function of the renormalization scale $\mu$. The solid line denotes the results of the present analysis (NLO) and of Ref. Alekhin:2017kpj (NNLO), the dashed line displays the ones derived using matching $\alpha_s^{\rm NLO}=\alpha_s^{\rm NNLO}$ at the scale $M_Z$ .
• Figure 3: The $\overline{\mathrm{MS}}\,$ values of the $t$-quark mass $m_t(m_t)$ obtained in the variants of the NLO ABMP16 fit with $\alpha_s^{(n_f=5)}(M_Z)$ fixed (squares) in comparison to ones at NNLO (circles). The left-tilted and right-tilted hatch represent the $1\sigma$ bands for $\alpha_s^{(n_f=5)}(M_Z)$ obtained in the ABMP16 nominal fits at NLO and NNLO, respectively. The points are slightly shifted left and right to prevent overlapping.
• Figure 4: The same as in Fig. \ref{['fig:scanmt']} for the $\overline{\mathrm{MS}}\,$ value of the $c$-quark mass $m_c(m_c)$.