Polarized Antimatter in the Proton from Global QCD Analysis

We present a global QCD analysis of spin-dependent parton distribution functions (PDFs) that includes the latest polarized $W$-lepton production data from the STAR collaboration at RHIC. These data allow the first data-driven extraction of a nonzero polarized light quark sea asymmetry $\Delta \bar{u} - \Delta \bar{d}$ within a global QCD framework with minimal theoretical assumptions. Within our simultaneous extraction of polarized PDFs, unpolarized PDFs, and pion and kaon fragmentation functions, we also extract a self-consistent set of antiquark polarization ratios $\Delta \bar{u}/\bar{u}$ and $\Delta \bar{d}/\bar{d}$.Comment: 4 figure