Direct bound on the minimal Universal Extra Dimension model from the $t\bar{t}$ resonance search at the Tevatron

TL;DR

This paper derives a new direct lower bound on the mass of the second KK gluon in the minimal Universal Extra Dimension model using Tevatron $tar{t}$ resonance search data, with implications for future LHC searches.

Contribution

It provides the first direct experimental bound on the second KK gluon mass in the mUED model from Tevatron data, focusing on the $tar{t}$ resonance channel.

Findings

Lower bound on $g^{(2)}$ mass above 800 GeV from Tevatron data.

Enhanced $g^{(2)} o tar{t}$ decay rate due to loop-induced vertices.

Discussion of future prospects at the LHC.

Abstract

In the minimal Universal Extra Dimension (mUED) model, the second Kaluza-Klein (KK) gluon $g^{(2)}$ has loop-induced vertices with the standard model quarks, mediated by the first KK modes of the quark and the gluon/Higgs boson. With a top quark pair, this vertex is enhanced by the cooperation of the strong coupling of a gluon and the large Yukawa coupling of a top quark, leading to substantial branching ratio of $Br(g^{(2)} \to t \bar{t}) \approx 7%-8%$. As the $g^{(2)}$ coupling with two gluons appears via dimension-6 operator, $q\bar{q}\to g^{(2)}\to t\bar{t}$ is the golden mode for the mUED model. Hence the best channel is the $t\bar{t}$ resonance search in $p\bar{p}$ collisions. The recent Tevatron data at $\sqrt{s}=1.96$ TeV with an integrated luminosity of 8.7 fb$^{-1}$ are shown to give the first direct bound on the $g^{(2)}$ mass above 800 GeV. The implication and future prospect at the LHC are discussed also.