Measurement of parity-violating spin asymmetries in W$^{\pm}$ production at midrapidity in longitudinally polarized $p$$+$$p$ collisions

TL;DR

This paper reports measurements of parity-violating spin asymmetries in W boson production in polarized proton-proton collisions, providing new insights into anti-quark helicity distributions at high energy.

Contribution

It presents the first high-statistics measurements of W asymmetries at midrapidity, significantly advancing knowledge of anti-quark polarized parton distribution functions.

Findings

Large parity-violating asymmetries observed

Data significantly exceeds previous measurements

Results inform anti-quark helicity distribution models

Abstract

We present measurements from the PHENIX experiment of large parity-violating single spin asymmetries of high transverse momentum electrons and positrons from $W^\pm/Z$ 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 anti-quark polarized parton distribution functions due to the parity-violating nature of the $W$-boson coupling to quarks and anti-quarks. The results presented are based on data collected in 2011, 2012, and 2013 with an integrated luminosity of 240 pb$^{-1}$, which exceeds previous PHENIX published results by a factor of more than 27. These high $Q^2$ data provide an important addition to our understanding of anti-quark parton helicity distribution functions.