Angular Correlations in Top Quark Pair Production and Decay at Hadron Colliders

TL;DR

The paper demonstrates that sizable angular correlations between the decay products of t and tbar can be observed at hadron colliders by exploiting a large asymmetry between like-spin and unlike-spin top pairs when using appropriate spin bases. It develops polarized production and decay formalisms, identifies effective spin analyzers (notably the charged lepton), and shows via parton-level Monte Carlo simulations that observable correlations survive realistic kinematic cuts. The analysis provides practical strategies to enhance spin-purity and to extract double-differential angular distributions, quantified by correlation parameters α_i and κ. It also discusses how potential new physics could alter these spin correlations, offering a pathway to probe beyond-Standard-Model interactions in top-quark events.

Abstract

We show how to observe sizable angular correlations between the decay products of the top quark and those of the anti-top quark in top quark pair production and decay at hadron colliders. These correlations result from the large asymmetry in the rate for producing like-spin versus unlike-spin top quark pairs provided the appropriate spin axes are used. The effects of new physics at production or decay on these correlations are briefly discussed.

Figures (12)

• Figure 1: Differential cross section for $t \bar{t}$ production as a function of the zero momentum frame speed $\beta$ of the top quark for the 2.0 TeV Tevatron (solid) and 14 TeV LHC (dashed).
• Figure 2: Differential cross section for $t \bar{t}$ production as a function of the $t \bar{t}$ invariant mass, $M_{t\bar{t}}$, for the Tevatron with center of mass energy 2.0 TeV, decomposed into ${\uparrow\downarrow}{+}{\downarrow\uparrow}$ and ${\uparrow\uparrow}{+}{\downarrow\downarrow}$ spins of the $t \bar{t}$ pair using the "beamline" basis for both $q \bar{q}$ and $gg$ components.
• Figure 3: Differential cross section for $t \bar{t}$ production as a function of the $t \bar{t}$ invariant mass, $M_{t\bar{t}}$, for the Tevatron with center of mass energy 2.0 TeV, decomposed into LR+RL and LL+RR helicities in the zero momentum frame of the $t \bar{t}$ pair for both $q \bar{q}$ and $gg$ components.
• Figure 4: Differential cross section for $t \bar{t}$ production as a function of the $t \bar{t}$ invariant mass, $M_{t\bar{t}}$, for the LHC with center of mass energy 14 TeV, decomposed into LR+RL and LL+RR helicities in the zero momentum frame of the $t \bar{t}$ pair for both $q \bar{q}$ and $gg$ components.
• Figure 5: The solid curve is the fraction of those $t \bar{t}$ pairs at the Tevatron (2.0 TeV) with an invariant mass above$M_{t\bar{t}}$ which have helicities LR$+$RL. The dashed curve is the fraction of the total cross section with an invariant mass above$M_{t\bar{t}}$.