Left-Handed W Bosons at the LHC

TL;DR

This paper demonstrates that at the LHC, W bosons produced with high transverse momentum are predominantly left-handed polarized, leading to observable asymmetries in decay products that can help distinguish backgrounds from new physics signals.

Contribution

It reveals the stable left-handed polarization of high-pt W bosons at the LHC and its potential use in separating backgrounds from new physics and top quark events.

Findings

High transverse momentum W bosons are strongly left-handed polarized.

Polarization leads to measurable asymmetries in decay product distributions.

Asymmetries are stable against QCD corrections.

Abstract

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 bosons translates the common left-handed polarization into a strong asymmetry in transverse momentum distributions between positrons and electrons, and between neutrinos and anti-neutrinos (missing transverse energy). Such asymmetries may provide an effective experimental handle on separating W + jets from top quark production, which exhibits very little asymmetry due to C invariance, and from various types of new physics.