Single Top Quark Production at the LHC: Understanding Spin

TL;DR

This paper investigates the polarization of single top quarks produced via Wg-fusion at the LHC, demonstrating the effectiveness of specific spin bases in analyzing top quark spin orientation.

Contribution

It introduces and compares the spectator jet and eta-beamline spin bases for analyzing top quark polarization in Wg-fusion production at 14 TeV.

Findings

High polarization in the chosen spin bases.

The spin bases remain effective after applying experimental cuts.

Helicity basis is less useful due to undefined zero momentum frame.

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.