Spin correlations: Tevatron vs. LHC

TL;DR

This paper compares how spin correlations in top quark pairs are observed at the Tevatron and LHC, highlighting different production mechanisms and strategies suited to each collider's environment.

Contribution

It analyzes the distinct spin correlation measurement strategies for top quark pairs at the Tevatron and LHC, emphasizing the different production processes and their implications.

Findings

Tevatron mainly produces t tbar via q qbar annihilation, requiring double-decay angle analysis.

LHC predominantly produces t tbar via gluon fusion, enabling azimuthal correlation measurements.

Lab frame measurements are feasible at the LHC for low-velocity t tbar pairs.

Abstract

We compare theoretical expectations for the observation of spin correlations in top quark pair production and decay at the Fermilab Tevatron and the CERN Large Hadron Collider (LHC). In particular, we note that the differing top quark pair production mechanisms in the two environments test different aspects of the Standard Model and require different strategies to observe the correlations. At the Tevatron, production is dominated by q qbar --> t tbar and the strategy is to construct a double-decay angle distribution where one decay angle is measured in the t rest frame and the other in the tbar rest frame. The dominant process at the LHC is gg --> t tbar, with a rich spin structure that allows for a second option in observing spin correlations. Here the strategy is to select events where the t tbar pair is produced at relatively low velocity in the zero momentum frame (ZMF). For these events, there are strong azimuthal correlations between t and tbar decay products present. This measurement enjoys the advantage that it can be carried out in the laboratory frame.