Manifestations of Top Compositeness at Colliders

TL;DR

The paper investigates right-handed top quark compositeness using an effective field theory with dimension-6 operators that modify top interactions, especially with gluons and four-top contact terms. It shows that inclusive $t\overline{t}$ rates at the Tevatron can be weakly constraining due to cancellations between operators, while kinematic distributions provide stronger bounds. It then analyzes four-top production at the LHC via a dimension-6 operator, finding sensitivity to compositeness scales up to ~5 TeV with 100 fb^{-1}. Overall, the work demonstrates the utility of a model-independent EFT approach for collider probes of top compositeness and highlights key observables that distinguish UV scenarios.

Abstract

We explore the possibility that the right-handed top quark is composite, identifying possible signatures of compositeness and how they might manifest themselves at the LHC and Tevatron. We perform a complete analysis of the dimension six modifications of the top coupling to gluons and find that cancellations among operators in the t\bar{t} rate allow for very low compositeness scales, but this can be drastically improved by looking at kinematic distributions. Turning to the LHC, we examine four top production from a dimension six four-top operator and estimate the LHC with 100 {\rm fb}^{-1} collected luminosity to be sensitive to compositeness scales as high as 5 TeV.

Figures (6)

• Figure 1: Feynman diagrams for the process $q\overline{q} \rightarrow t \overline{t}$. The shaded blob in the diagram on the right represents the insertion of the new physics $g$-$t$-$\overline{t}$ vertex.
• Figure 2: The inclusive top pair production cross section in the plane of $g_1$ and $g_2$. The region between the two black lines is consistent with Tevatron $t\overline{t}$ cross section measurements at $1\sigma$, and the Standard Model prediction is represented by the black square. The black triangles denote two points which lead to a cross section within $1\sigma$ of the experimental results, and for which we present detailed distributions in Figure \ref{['fig:PT2Mass']}.
• Figure 3: Invariant mass distribution of $t\overline{t}$ for (g1= g2 = 0.11) and (g1 = -2.0, g2 = 1.3)
• Figure 4: Rapidity distribution of the top quark for (g1= g2 = 0.11) and (g1 = -2.0, g2 = 1.3)
• Figure 5: Representative Feynman diagram illustrating the contribution from a four top operator to four top production at the LHC.