Spin configuration of top quark pair production with large extra dimensions at photon-photon colliders

TL;DR

This paper investigates how large extra dimensions affect top quark pair production and spin asymmetries at photon-photon colliders, proposing new observables to detect quantum gravity effects and setting bounds on the gravity scale.

Contribution

It introduces a novel top spin asymmetry observable sensitive to extra dimensions and identifies a special spin basis where standard model effects vanish, enhancing detection potential.

Findings

Top spin asymmetry vanishes in the standard model but not with extra dimensions.

Lower bounds on the quantum gravity scale $M_S$ are established using various polarization configurations.

Unpolarized measurements of the top spin state improve bounds on $M_S$ by about 5%.

Abstract

Top quark pair production at photon-photon colliders is studied in low scale quantum gravity scenario. From the dependence of the cross sections on the spin configuration of the top quark and anti-quark, we introduce a new observable, top spin asymmetry. It is shown that there exists a special top spin basis where with the polarized parent electron beams the top spin asymmetry vanishes in the standard model but retains substantial values with the large extra dimension effects. We also present lower bounds of the quantum gravity scale $M_S$ from total cross sections with various combinations of the laser, electron beam, and top quark pair polarizations. The measurements of the top spin state $(t_\uparrow\bar{t}_\downarrow)$ with unpolarized initial beams are shown to be most effective, enhancing by about 5% the $M_S$ bounds with respect to totally unpolarized case.