Isospin asymmetry of quark distributions and implications for single top-quark production at the LHC

Abstract

We present an improved determination of the up-and down-quark distributions in the proton using recent data on charged lepton asymmetries from W AE gauge-boson production at the LHC and Tevatron. The analysis is performed in the framework of a global fit of parton distribution functions. The fit results are consistent with a nonzero isospin asymmetry of the sea, xðd − uÞ, at small values of Bjorken x ∼ 10 −4 indicating a delayed onset of the Regge asymptotics of a vanishing ðd − uÞ-asymmetry at small x. We compare with up-and down-quark distributions available in the literature and provide accurate predictions for the production of single top-quarks at the LHC, a process which can serve as a standard candle for the light quark flavor content of the proton.

Strange and non-strange distributions from the collider data

“…It is worth noting that the charm production data [3,4] are well described in this variant of fit, with χ 2 /NDP = 167/226 achieved 1 . It is interesting to see that the strange sea distribution obtained with the ABMP16 PDF shape and the same data selection is significantly smaller at x ∼ 0.1 and agrees with the nominal ABMP16 1 The value of χ 2 for the CCFR/NuTeV data is smaller than the number of data points (NDP) due to the definition of the experimental covariance matrix, which includes effects of neighbor bin correlations, so that the effective number of degrees of freedom is smaller than the number of data points, see Ref. [3] for details.…”

“…These samples, together with the DY data obtained at the Tevatron collider in the forward region, probe PDFs at values of x down to 10 −4 and therefore provide a supplementary constraint to the HERA inclusive data. This potential was in particular employed in the ABMP PDF fit in order to disentangle small-x uand d-quark distributions [1,2]. The impact of the collider DY data on this piece is very significant.…”

Measurement of associated production of a $$\mathrm {W}$$ W boson and a charm quark in proton–proton collisions at $$\sqrt{s} = 13\,\text {Te}\text {V} $$ s

“…In these references, the treatment of the sea quark distributions in different PDF sets is discussed, and the comparison of the PDFs is presented. The ABMP16nlo PDF includes the most recent data on charm quark production in chargedcurrent neutrino-nucleon DIS collected by the NOMAD and CHORUS experiments in order to improve the constraints on the strange quark distribution and to perform a detailed study of the isospin asymmetry of the light quarks in the proton sea [56]. Despite differences in the data used in the individual global PDF fits, the strangeness suppression distributions in ABMP16nlo, NNPDF3.1nlo, CT14nlo and MMHT14nlo are in a good agreement among each other and disagree with the ATLASepWZ16nnlo result [14].…”

The new ABM16 PDFs

“…This input is particularly useful for the extraction of the d-quark distribution at large x since it allows to avoid uncertainties due to the modeling of nuclear effects, which appear in case of employing the DIS deuteron data for this purpose. The statistical accuracy of the d-quark distribution, which can be achieved using the DY data is comparable to the one for the existing DIS deuteron data sets used earlier in the ABM12 fit [2]. Therefore, in the present analysis we skip the latter in order to reduce theoretical uncertainties keeping the overall one on the same level, cf.…”