The production of $W$ bosons in association with jets is an important background to new physics at the LHC. Events in which the $W$ carries large transverse momentum and decays leptonically lead to large missing energy and are of particular importance. We show that the left-handed nature of the $W$ coupling, combined with valence quark domination at a $pp$ machine, leads to a large left-handed polarization for both $W^{+}$ and $W^{-}$ bosons at large transverse momenta. The polarization fractions are very stable with respect to QCD corrections. The leptonic decay of the $W^{\pm }$ bosons translates the common left-handed polarization into a strong asymmetry in transverse momentum distributions between positrons and electrons and between neutrinos and antineutrinos (missing transverse energy). Such asymmetries may provide an effective experimental handle on separating $W+\mathrm{\text{jets}}$ from top-quark production, which exhibits very little asymmetry due to C invariance, and from various types of new physics.

• Received 24 April 2011

DOI:https://doi.org/10.1103/PhysRevD.84.034008