Top quark spin correlations in the Randall-Sundrum model at the CERN Large Hadron Collider

In the Randall-Sundrum model, we study top-antitop pair production and top spin correlations at the Large Hadron Collider. In addition to the standard model processes, there is a new contribution to the top-antitop pair production process mediated by graviton Kaluza-Klein modes in the $s$-channel. We calculate the density matrix for the top-antitop pair production including the new contribution. With a reasonable parameter choice in the Randall-Sundrum model, we find a sizable deviation of the top-antitop pair production cross section and the top spin correlations from those in the standard model. In particular, resonant productions of the graviton Kaluza-Klein modes give rise to a remarkable enhancement of such a deviation.

Figure 1

The dependence of the cross section of the top-antitop quark pair production by quark-antiquark pair annihilation on the center-of-mass energy of colliding partons. The solid line and dashed lines correspond to the results of the SM and the RS model for $m_1=600\mathrm{GeV}$ and $\kappa /{\overline{M}}_{\mathrm{pl}}=0.01$, 0.04, 0.07 and 0.1 from bottom to top, respectively.

Figure 2

The dependence of the cross section of the top-antitop quark pair production by gluon fusion on the center-of-mass energy of colliding partons. The solid line and dashed lines correspond to the results of the SM and the RS model for $m_1=600\mathrm{GeV}$ and $\kappa /{\overline{M}}_{\mathrm{pl}}=0.01$, 0.04, 0.07 and 0.1 from bottom to top, respectively.

Figure 3

Differential cross section (4.1) as a function of $\cos \theta$ with $E_{\mathrm{CMS}}=14\mathrm{TeV}$ for $m_1=600\mathrm{GeV}$ and $\kappa /{\overline{M}}_{\mathrm{pl}}=0.1$. The solid line and dashed line correspond to the results of the SM and the RS model, respectively. The differential cross sections for the like (dotted) and the unlike (dash-dotted) top-antitop spin pair productions in the RS model are also depicted.

Figure 4

Differential cross section (4.2) as a function of the top-antitop invariant mass $M_{t\overline{t}}$ for $m_1=600\mathrm{GeV}$ and $\kappa /{\overline{M}}_{\mathrm{pl}}=0.1$. The solid and dashed lines correspond to the results of the SM and the RS model, respectively. The differential cross sections for the like (dotted) and the unlike (dash-dotted) top-antitop spin pair productions in the RS model are also depicted.

Figure 5

Differential cross section (4.2) as a function of the top-antitop invariant mass $M_{t\overline{t}}$. The solid and dashed lines correspond to the results of the SM and the RS model with $\kappa /{\overline{M}}_{\mathrm{pl}}=0.01$, 0.04, 0.07 and 0.1 from bottom to top, respectively.

Figure 6

Spin asymmetry $\mathcal{A}$ as a function of the top-antitop invariant mass $M_{t\overline{t}}$. The solid line corresponds to the SM, while the dashed lines correspond to the RS model with $\kappa /{\overline{M}}_{\mathrm{pl}}=0.01$, 0.04, 0.07 and 0.1 from up to down, respectively.

Figure 7

Spin asymmetry $\mathcal{A}$ as a function of $\kappa /{\overline{M}}_{\mathrm{pl}}$ at the LHC with $E_{\mathrm{CMS}}=14\mathrm{TeV}$. As $\kappa /{\overline{M}}_{\mathrm{pl}}\to 0$, $\mathcal{A}$ becomes the SM value, 0.319.