Single transverse-spin asymmetry in hadronic dijet production

Abstract

We study the single-transverse-spin asymmetry for dijet production in hadronic collisions in both the collinear QCD factorization approach and the Brodsky-Hwang-Schmidt model. We show that a nonvanishing asymmetry is generated by both initial-state and final-state interactions, and that the final-state interactions dominate. We find that in the leading kinematic region where the transverse momentum imbalance of the two jets, ${\stackrel{\ensuremath{\rightarrow}}{q}}_{\ensuremath{\perp}}={\stackrel{\ensuremath{\rightarrow}}{P}}_{1\ensuremath{\perp}}+{\stackrel{\ensuremath{\rightarrow}}{P}}_{2\ensuremath{\perp}}$, is much less than the momentum of either jet, the contribution from the lowest nontrivial perturbative order to both the spin-averaged and the spin-dependent dijet cross sections can be factorized into a hard part that is a function only of the averaged jet momentum ${\stackrel{\ensuremath{\rightarrow}}{P}}_{\ensuremath{\perp}}=({\stackrel{\ensuremath{\rightarrow}}{P}}_{1\ensuremath{\perp}}\ensuremath{-}{\stackrel{\ensuremath{\rightarrow}}{P}}_{2\ensuremath{\perp}})/2$, and perturbatively generated transverse momentum dependent (TMD) parton distributions. We show that the spin asymmetry at this nontrivial perturbative order can be described by the TMD parton distributions defined in either semi-inclusive deep inelastic scattering or the Drell-Yan process. We derive the same hard parts from both the collinear factorization approach and in the context of the Brodsky-Hwang-Schmidt model, verifying that they are not sensitive to details of the factorized long-distance physics.