Improved measurement of thed¯/ūasymmetry in the nucleon sea

Abstract

Measurements of the ratio of Drell-Yan yields from an 800 GeV/c proton beam incident on liquid hydrogen and deuterium targets are reported. Approximately 360,000 Drell-Yan muon pairs remained after all cuts on the data. ¿From these data, the ratio of anti-down (d) to anti-up (ū) quark distributions in the proton sea is determined over a wide range in Bjorken-x. These results confirm previous measurements by E866 and extend them to lower x. From these data, (d −ū) and (d −ū)dx are evaluated for 0.015 < x < 0.35. These results are compared with parameterizations of various parton distribution functions, models and experimental results from NA51, NMC and HERMES. 13.85.Qk; 14.20.Dh; 24.85.+p; 14.65.Bt

QCD analysis of the ATLAS and CMS W± and Z cross-section measurements and implications for the strange sea density

“…One further cross-check of the robustness of the present result is performed. For the CSKK fit,d −ū at x ∼ 0.1 is negative, approximately 2-3 standard deviations away from the positive value suggested by the E866 fixedtarget Drell-Yan data [17]. It has been suggested that if positive (d −ū) were imposed on the fit [16], the strangeness would decrease since largerd is correlated to smaller strangeness in the current parametrization.…”

“…Thus it seems that the collider data do favor a larger strangeness ratio than neutrino di-muon data. The ABM group [16] has made a study which focuses on the potential incompatibility of a large strangeness ratio with the positive value ofd −ū at x ∼ 0.1 observed by E866 [17]. This is addressed at the end of Sec.…”

Measurement of theW→eνandZ/γ*→e+e−Adamczyk1, Agakishiev2, Aggarwal3 et al. 2012Phys. Rev. DSelf Cite242130View full textAdd to dashboardCite

“…Drell-Yan experiments [17,18] have measured a large asymmetry in this x range, and precision measurements of R W at RHIC can provide independent constraints on the flavor asymmetry which are free from the assumption of charge symmetry required in Drell-Yan. Measurements of the lepton charge asymmetry at the LHC [33,34] provide similar constraints on the quark and antiquark PDFs, though at significantly lower x due to the much higher energy of the collisions.…”

“…Comparable distributions for the antiquarks within the proton sea, however, are much more weakly constrained. Interest in these poorly-known antiquark PDF's has also increased over the last few years, due to results from Drell-Yan experiments [17,18] which find evidence for a much largerd/ū flavor asymmetry in the nucleon than had been anticipated, especially at momentum fractions near and above x ∼ 0.2. Detailed measurements of W ± and Z/γ * production in proton-proton collisions will provide new and complementary information about this flavor asymmetry in the sea, from different reactions and at very different momentum scales.…”

Parton distributions for the LHC run II

“…ZEUS HERA-II DIS cross-sections [33,34]; CHORUS inclusive neutrino DIS [35], and NuTeV dimuon production data [36,37]; fixed-target E605 [38] and E866 [39][40][41] DrellYan production data; CDF W asymmetry [42] and CDF [43] and D0 [44] Z rapidity distributions; CDF [45] and D0 [46] Run-II one-jet inclusive cross-sections; ATLAS [47], CMS [48] and LHCb [49] data on vector boson production; and ATLAS one-jet inclusive cross-sections [50] from the 2010 run. In NNPDF3.0, several new datasets have been included.…”