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Nuclear Physics Seminars at BNL

Asymmetry of antimatter in the proton from SeaQuest and SpinQuest perspectives

by Kei Nagai (Los Alamos National Laboratory)


Naively, the amounts of dbar and ubar in the proton were expected to be the same based
on the flavor-independence of the strong coupling. However, the muon deep inelastic
scattering experiment NMC at CERN found dbar>ubar in the proton. Drell--Yan
experiments also obtained the results consistent with it. The Drell--Yan experiment
E866 at Fermilab showed that dbar(x)/ubar(x)>1.0 for 0.015 < x < 0.20. It
also showed dbar(x)/ubar(x)<1.0 at large x (x~0.3), although it is
consistent with 1.0 within statistical uncertainty. SeaQuest is a Drell--Yan experiment
at Fermilab that measured the antiquark flavor asymmetry dbar/ubar
precisely for a wide x range (0.13 < x < 0.45) including the intriguing
region in from E866. It uses a 120 GeV proton beam extracted from Fermilab Main Injector
colliding with liquid hydrogen and deuterium targets. The antiquark flavor asymmetry
dbar(x)/ubar(x) is derived from the cross section ratio of proton-deuterium
to proton-proton Drell--Yan processes. 
SeaQuest results were published on Nature in February 2021. In this talk, the contents of Nature paper will be mainly presented.
In addition to that, the perspective of the SpinQuest experiment will be also discussed.