The ABM parton distributions tuned to LHC data

Abstract

We present a global fit of parton distributions at next-to-next-to-leading order (NNLO) in QCD. The fit is based on the world data for deep-inelastic scattering, fixed-target data for the Drell-Yan process and includes, for the first time, data from the Large Hadron Collider (LHC) for the Drell-Yan process and the hadro-production of top-quark pairs. The analysis applies the fixed-flavor number scheme for n_f=3,4,5, uses the MS-bar scheme for the strong coupling \alpha_s and the heavy-quark masses and keeps full account of the correlations among all non-perturbative parameters. At NNLO this returns the values of \alpha_s(M_Z) = 0.1132 +- 0.0011 and m_t(pole) = 171.2 +- 2.4 GeV for the top-quark pole mass.The fit results are used to compute benchmark cross sections for Higgs production at the LHC to NNLO accuracy. We compare our results to those obtained by other groups and show that differences can be linked to different theoretical descriptions of the underlying physical processes.Comment: 31 pages, 15 figure

Determination of strange sea quark distributions from fixed-target and collider data

“…The description of the DIS data employs the three-flavor factorization scheme with the heavy c-and b-quarks appearing in the final state only. This approach provides a good agreement with the existing inclusive neutralcurrent (NC) DIS data up to the highest momentum transfer Q 2 covered by HERA [18]. In particular, such an agreement is related to the use of the massive NNLO corrections for the NC heavy-quark production, along with the MS definition of the heavy-quark masses [21,22].…”

“…[18] and references therein). The flavor separation of the u-and d-quark distributions in the nucleon is obtained with a good accuracy from the combination of proton and deuteron fixed-target data with the LHC data on W-and Z-boson production.…”

“…The former results have been derived for heavy-quark masses in the on-shell renormalization. 2 For consistency with the setup of the ABM fit [17,18] which uses the MS definition for heavy-quark masses in DIS [21,22] for an improved convergence and better stability under scale variation, we briefly summarize below those changes from the pole mass scheme to the MS scheme which are necessary if the NNLO Wilson coefficients C ð2Þ k;i at asymptotically large values ξ ¼ Q 2 =m 2 c are included. The conversion uses the well-known relation between the pole mass m c and the running mass mðμ r Þ in the MS scheme…”

“…Section II introduces the framework of the analysis, which is based on a global fit of PDFs by ABM [16][17][18] using the world DIS data and the measurements of gauge-boson production from fixed targets and the LHC. Section II also summarizes briefly the new improvements in QCD theory for CC DIS charm quark production with a running c-quark mass.…”

Determination ofαsfrom the QCD static energy: An update

“…[48]; and the PDF-fit ABM13 result of Ref. [49] (note that the error bars in this case do not include effects from higher unknown perturbative orders). We also show the lattice average by the FLAG collaboration [41] and the PDG average excluding lattice results [2] -black points-.…”