QCD Corrections to Double and Single Spin Asymmetries in Vector Boson Production at Polarized Hadron Colliders

TL;DR

This work provides a complete next-to-leading order QCD calculation of the double and single spin asymmetries in W±/Z0 production from polarized hadron collisions. By deriving the O(αs) corrections within the MSbar scheme using the HVBM γ5 prescription, the authors express the cross sections as convolutions of polarized and unpolarized PDFs with analytic coefficient functions, validating the results through consistency with polarized Drell–Yan and Kamal’s inclusive cross-section findings. The numerical study demonstrates that NLO corrections can be sizable, especially for A_L(y<0) and A_LL(y), and emphasizes that precise extractions of polarized quark distributions require knowledge of the polarized gluon distribution ΔG. The analysis shows that scale variations induce only small changes in the asymmetries, while ΔG remains the dominant source of theoretical uncertainty for certain observables, highlighting the need for complementary measurements to constrain polarized gluons at RHIC.

Abstract

The production of $W^{\pm}$ and $Z^0$ bosons in collisions of longitudinally polarized protons allows to access various combinations of the polarized quark distributions from the study of double and single spin asymmetries. We compute the ${\cal O}(α_s)$ corrections to these asymmetries as function of the vector boson rapidity $y$ in the hadron-hadron centre-of-mass frame. Detailed studies of the numerical impact of the next-to-leading order corrections are presented. The theoretical uncertainties of an extraction of polarized quark distributions from future vector boson production data are investigated in detail.

Figures (4)

• Figure 1: Unpolarized vector boson production cross sections in proton-proton collisions at RHIC ($\sqrt S = 500$ GeV).
• Figure 2: Predictions for double (left) and single (right) spin asymmetries in vector boson production in $pp$ collisions at $\sqrt s = 500$ GeV obtained for different parameterizations of the next-to-leading order polarized parton densities.
• Figure 3: Contributions of the individual parton level subprocesses to the double (left) and single (right) polarized vector boson production cross sections in $pp$ collisions at $\sqrt s = 500$ GeV. All polarized cross sections are normalized to the full unpolarized cross section at next-to-leading order.
• Figure 4: Variation of the double (left) and single (right) spin asymmetries in vector boson production in $pp$ collisions at $\sqrt s = 500$ GeV under variation of the mass factorization scale.