Top Spin Correlations in Theories with Large Extra-Dimensions at the Large Hadron Collider

TL;DR

The paper investigates how large extra dimensions in the ADD model, via virtual KK graviton exchange in the s-channel, modify top-antitop production and spin correlations at the LHC. It derives the full density matrix for $t\bar{t}$ production in both $q\bar{q}$ and $gg$ channels and analyzes observables using an EFT with $f_G=\pi\lambda/(2 M_D^4)$ and $\lambda=\pm 1$, applying a $\sqrt{s}\le M_D$ cutoff for validity. The authors find sizable deviations in cross sections and the top-spin asymmetry ${\cal A}$ for $M_D\lesssim 2$ TeV, dominated by gluon fusion and sensitive to the sign of $\lambda$, with leptonic angular correlations providing measurable discrimination. These results offer collider-based constraints on the fundamental scale of extra dimensions through top-spin observables at the LHC.

Abstract

In theories with large extra dimensions, we study the top spin correlations at the Large Hadron Collider. The s-channel process mediated by graviton Kaluza-Klein modes contributes to the top-antitop pair production in addition to the Standard Model processes, and affects the resultant top spin correlations. We calculated the full density matrix for the top-antitop pair production. With the fundamental scale of the extra dimensional theory below 2 TeV, we find a sizable deviation of the top spin correlations from the Standard Model one.

Figures (10)

• Figure 1: The dependence of the total cross section of the top-antitop quark pair production on the center-of-mass energy of colliding partons. The solid line and the dashed line correspond to the SM prediction for the $q\bar{q}\rightarrow t\bar{t}$ and the $gg\rightarrow t\bar{t}$ channels, respectively. The dash-dotted line and the dotted line correspond to the predictions of the ADD model for the same channels with $\lambda=1$ and $M_D=1$ TeV.
• Figure 2: Total cross section for the top pair production as a function of the scale $M_D$ for the LHC with center-of-mass energy $14$ TeV. The horizontal line corresponds to the prediction of the SM, and the solid (dotted) line to the ADD model in $\lambda=1$ ($\lambda=-1$) case with the cut. The dashed (dash-dotted) line depicts the plot in $\lambda=1$ ($\lambda=-1$) case without the cut.
• Figure 3: The breakdown of the total cross section into the like (dotted) and the unlike (dash-dotted) top-antitop spin pairs in the ADD model besides the total cross section of the SM (horizontal lines) and the ADD model (dashed lines) results with $M_D=1$ TeV and $E_{CMS}=14$ TeV.
• Figure 4: Differential cross section (\ref{['total_cosTheta']}) as a function of $\cos\theta$ with $M_D=1$ TeV and $E_{CMS}=14$ TeV. The solid lines and dashed lines correspond to the results of the SM and the ADD model, respectively. The differential cross sections for the like (dotted) and the unlike (dash-dotted) top-antitop spin pair productions in the ADD model are also depicted.
• Figure 5: Differential cross sections (\ref{['total_s']}) as a function of the center-of-mass energy of colliding partons $\sqrt{s}\leq M_D$. The solid and dashed lines correspond to the results of the SM and the ADD model, respectively. The differential cross sections for the like (dotted) and the unlike (dash-dotted) top-antitop spin pair productions in the ADD model are also depicted.