Top Compositeness at the Tevatron and LHC

TL;DR

The paper investigates the possibility that the right-handed top quark is composite, using a bottom-up EFT with a leading dimension-6 four-top operator and potential heavy vector resonances. It shows that Tevatron tt̄ production only weakly constrains the compositeness scale, allowing Λ/g roughly in the few-hundred-GeV range, while differential distributions could tighten this bound. At the LHC, four-top production via a heavy ρ resonance can be dramatically enhanced, and a conservative like-sign dilepton + jets analysis with high-H_T cuts indicates discovery reach up to about 2 TeV for color-octet or strongly coupled singlet states with 100 fb⁻¹. The study highlights observable handles such as jet and b-jet multiplicities and lepton-charge balance to distinguish a four-top signal from backgrounds and alternative new-physics scenarios, underscoring the LHC’s potential to reveal or constrain top compositeness across wide parameter space.

Abstract

We explore the possibility that the right-handed top quark is composite. We examine the consequences that compositeness would have on $t \bar{t}$ production at the Tevatron, and derive a weak constraint on the scale of compositeness of order a few hundred GeV from the $t \bar{t}$ inclusive cross section. More detailed studies of differential properties of $t \bar{t}$ production could potentially improve this limit. We find that a composite top can result in an enhancement of the $t \bar{t} t \bar{t}$ production rate at the LHC (of as much as $10^3$ compared to the Standatd Model four top rate). We explore observables which allow us to extract the four top rate from the backgrounds, and show that the LHC can either discover or constrain top compositeness for wide ranges of parameter space.

Figures (4)

• Figure 1: Representative Feynman Diagram showing how the four top quark operator can contribute to $q \overline{q} \rightarrow t \overline{t}$ at one loop.
• Figure 2: Invariant mass distribution of $p \overline{p} \to t\overline t$ at the Tevatron run II, both in the Standard Model, and including the singlet-mediated contact interaction with $g = 4\pi$, for $\Lambda = 500$ GeV and $\Lambda = 1$ TeV.
• Figure 3: The rate for $t \overline{t} t \overline{t}$ at the LHC as a function of mass $M$ for several values of the coupling $g = 2\pi, 1, 0.1$ (from top to bottom), for both the case where the $\rho$ is a color octet (solid lines) or a singlet (dashed lines). Also shown for reference is the SM 4 top production rate.
• Figure 4: Differential cross section for the signal (with $M=1$ TeV and $g=2\pi$) and SM backgrounds with respect to the number of hard jets (upper left), number of $b$-tagged jets (upper right), $H_t$ (lower left), and missing transverse momentum (lower right). The $H_t$ distribution is plotted before the $H_t$ cut is applied; the other three distributions include all of the cuts.