Single Top Quark Production at the LHC: Understanding Spin

Abstract

We show that the single top quarks produced in the Wg-fusion channel at a proton-proton collider at a center-of-mass energy sqrt{s}=14 TeV posses a high degree of polarization in terms of a spin basis which decomposes the top quark spin in its rest frame along the direction of the spectator jet. A second useful spin basis is the eta-beamline basis, which decomposes the top quark spin along one of the two beam directions, depending on which hemisphere contains the spectator jet. We elucidate the interplay between the two- and three-body final states contributing to this production cross section in the context of determining the spin decomposition of the top quarks, and argue that the zero momentum frame helicity is undefined. We show that the usefulness of the spectator and eta-beamline spin bases is not adversely affected by the cuts required to separate the Wg-fusion signal from the background.

Figures (3)

• Figure 1: Representative Feynman diagrams for single top quark production via $Wg$ fusion.
• Figure 2: The differential cross sections (total, LAB helicity basis left, spectator basis up, and $\eta$-beamline basis up (with $\eta_{min}=0$)) as a function of the top quark transverse momentum for single top quark production via $Wg$ fusion at the LHC with a center of mass energy of 14 TeV.
• Figure 3: The differential cross sections (total, LAB helicity basis right, spectator basis down, and $\eta$-beamline basis down (with $\eta_{min}=0$)) as a function of the top antiquark transverse momentum for single top antiquark production via $Wg$ fusion at the LHC with a center of mass energy of 14 TeV.