Maximizing the spin correlation of top quark pairs produced at the LHC

TL;DR

This work aims to maximize top-quark pair spin correlation at the LHC within the Standard Model by constructing a quantization axis that optimizes the spin-density-matrix–based correlation. It shows that diagonalizing the spin-correlation matrix $C_{ij}$ yields an event-by-event optimal axis for gluon fusion, achieving near-maximal correlation, while the quark–antiquark channel attains 100% correlation along its optimal axis. LO results indicate $C_{ ext{max}}$ ≈ 0.48 without cuts and ≈0.50 with a kinematic cut, with only modest scale dependence. The approach provides a practical enhancement for observing top spin correlations at the LHC and has implications for precision tests of the SM and new-physics searches in the top sector.

Abstract

The measurement of top quark spin correlation is an important tool for precise studies of top quark interactions. In this letter I construct a quantization axis maximizing the spin correlation at the LHC within the Standard Model. Using this axis a spin correlation of 48% or even more, on applying additional cuts, can be reached. This represents a significant improvement compared to the helicity bases studied thus far.