We present midrapidity measurements from the PHENIX experiment of large parity-violating single-spin asymmetries of high transverse momentum electrons and positrons from ${\mathrm{W}}^{\pm }/\mathrm{Z}$ decays, produced in longitudinally polarized $p+p$ collisions at center of mass energies of $\sqrt{s}=500$ and 510 GeV. These asymmetries allow direct access to the antiquark polarized parton distribution functions due to the parity-violating nature of the $\mathrm{W}$-boson coupling to quarks and antiquarks. The results presented are based on data collected in 2011, 2012, and 2013 with an integrated luminosity of $240{\mathrm{pb}}^{-1}$, which exceeds previous PHENIX published results by a factor of more than 27. These high $Q^2$ data probe the parton structure of the proton at W mass scale and provide an important addition to our understanding of the antiquark parton helicity distribution functions at an intermediate Bjorken $x$ value of roughly $M_{\mathrm{W}}/\sqrt{s}=0.16$.

• Received 29 April 2015

DOI:https://doi.org/10.1103/PhysRevD.93.051103