Searching for the Kaluza-Klein Graviton in Bulk RS Models

TL;DR

The paper evaluates the LHC prospects for discovering the lightest Kaluza-Klein graviton in Randall-Sundrum models where SM fields propagate in the bulk and the right-handed top is IR-localized while lighter fermions sit near the Planck brane. It computes production cross sections (dominated by gg G) and decay widths ( dominated by tt and TeV-scale scalars), highlighting a very narrow graviton resonance and the potential to determine its spin-2 nature via tt angular distributions. The authors estimate a discovery reach around m_grav pprox 1.7 TeV under 100 fb$^{-1}$ with ideal top tagging, and discuss boosted-top tagging strategies and challenges in the highly boosted regime. They argue that spin-2 identification provides a distinctive smoking gun for RS-type new physics and outline areas for further experimental and model-building refinement.

Abstract

The best-studied version of the RS1 model has all the Standard Model particles confined to the TeV brane. However, recent variants have the Standard Model fermions and gauge bosons located in the bulk five-dimensional spacetime. We study the potential reach of the LHC in searching for the lightest KK partner of the graviton in the most promising such models in which the right-handed top is localized very near the TeV brane and the light fermions are localized near the Planck brane. We consider both detection and the establishment of the spin-2 nature of the resonance should it be found.

Figures (6)

• Figure 1: Cross section of KK graviton production with $M_4 L=2.5$. Both the cross-section from gluon fusion $gg\rightarrow G$ and W boson fusion $qq \rightarrow q'q' WW \rightarrow q'q' G$ are shown.
• Figure 2: Branching Ratios for graviton decay to scalars and quarks as a function of the top-right localization parameter $\nu_{t,R}$. At $-0.5 < \nu_{t,R}< -0.2$, the dominant decay is to the Higgs and longitudinal gauge bosons $Z_L,W_L^\pm$. At $\nu_{t,R} > -0.2$, the dominant decay is to $t\bar{t}$. The decay to a zero-mode top and a KK anti-top is kinematically allowed in the range $-0.5 < \nu_{t,R} < 0.5$. The line at $\nu_{t,R}$ corresponds to the specific choice made in agashe.
• Figure 3: The $s/\sqrt{b}=5$ reach as a function of graviton mass and the parameter $(M_4 L)$. From top to bottom, the reach is shown for 100%, 10%, and 1% efficient top identification. Different levels of top IR localization are shown, $\nu_{t,R}=10.0,1.0,0.5,0.0$. Larger $\nu_{t,R}$ corresponds to a more IR-localized $t_R$.
• Figure 4: Distributions of $\Delta R$ of top decay products for various KK masses.
• Figure 5: Generic Sample of 100 $gg \rightarrow G \rightarrow t\bar{t}$ events. The results of a Monte Carlo of 100 spin-2 events are shown on top of the expected results for a spin-0, spin-1, and spin-2 resonance. Events have been removed both from the expected curves and the Monte Carlo events if they are too close to forward or backward scattering to be likely to be observed (that is, if pseudo-rapidity $\eta > 2.5 - \ln 2$).