Collider Implications of Universal Extra Dimensions

Abstract

We consider the universal extra dimensions scenario of Appelquist, Cheng, and Dobrescu, in which all of the SM fields propagate into one extra compact dimension, estimated therein to be as large as $\sim (350$ GeV$)^{-1}$. Tree-level KK number conservation dictates that the associated KK excitations can not be singly produced. We calculate the cross sections for the direct production of KK excitations of the gluon, $\gs$, and two distinct towers of quarks, \qs and $\qt$, in proton-antiproton collisions at the Tevatron Run I and II energies in addition to proton-proton collisions at the Large Hadron Collider energy. The experimental signatures for these processes depend on the stability of the lowest-lying KK excitations of the gluons and light quarks. We find that the Tevatron Run I mass bound for KK quark and gluon final states is about 350--400 GeV, while Run II can push this up to 450--500 GeV at its initial luminosity and 500--550 GeV if the projected final luminosity is reached. The LHC can probe much further: The LHC will either discover UED KK excitations of quarks and gluons or extend the mass limit to about 3 TeV.

Figures (9)

• Figure 1: Relative coupling strengths of vertices involving $q_{n}^{\bullet}$'s and $q_{n}^{\circ}$'s. Only the overall factors are shown: These vertices also involve the usual SU($3$) matrix element and the Dirac $\gamma_{\mu}$ matrix. Here, $n$ and $m$ are distinct positive integers ($n \neq m$) and the projection operators are defined as $P_{L,R}\equiv(1 \mp \gamma_5)/2$.
• Figure 2: The cross section for the production of two stable KK final states is shown as a function of the KK mass for Tevatron Run I (top) and II (bottom). The solid curve corresponds to the total contribution, while the dashed lines represent the partial contributions of KK quark pair ($\square$), KK quark-gluon ($\vartriangle$), and KK gluon pair ($\triangledown$) production. Also shown is top production ($+$), which features a different collider signature (namely, the top will subsequently decay into additional states). Solid horizontal lines mark $100$ events at the initial and final projected luminosities for Run II.
• Figure 3: The same as Fig. \ref{['fig:fTev']}, but for the LHC. The solid horizontal line represents $100$ annual events at the projected luminosity.
• Figure 4: The decays of the $q_1^{\bullet}$ or $q_1^{\circ}$ (solid) and $g_1^{\star}$ (dashed) into SM fields via graviton emission (spin $2$ and scalar combined) are shown as a function of the compactification scale $\mu = M = 1/R$ for $M_D = 5$ TeV. The pairs of curves correspond to $2$, $4$, and $6$ extra dimensions from top to bottom, respectively.
• Figure 5: The graviton mass distribution (top) and missing energy distribution (bottom) of the $q_1^{\bullet}$ or $q_1^{\circ}$ (solid) and $g_1^{\star}$ (dashed) are illustrated for $\mu = 500$ GeV and $M_D = 5 TeV$. The pairs of curves correspond to $2$, $4$, and $6$ extra dimensions.