Collider Implications of Kaluza-Klein Excitations of the Gluons

Abstract

We consider an asymmetric string compactification scenario in which the SM gauge bosons can propagate into one TeV$^{-1}$-size extra compact dimension. These gauge bosons have associated KK excitations that present additional contributions to the SM processes. We calculate the effects that the KK excitations of the gluons, $g^{\star}$'s, have on multijet final state production in proton-proton collisions at the Large Hadron Collider energy. In the case of dijet final states with very high $p_{{}_T}$, the KK signal due to the exchanges of the $g^{\star}$'s is several factors greater than the SM background for compactification scales as high as about 7 TeV. The high-$p_{{}_T}$ effect is not as dramatic for the direct production of a single on-shell $g^{\star}$, which subsequently decays into $q$-$\bar{q}$ pairs, where the KK signal significantly exceeds the SM three-jet background for compactification scales up to about 3 TeV. We also present our results for the four-jet final state signal from the direct production of two on-shell $g^{\star}$'s.

Figures (16)

• Figure 1: Relative coupling strengths of vertices involving $g^{\star}$'s. Only the overall factors are shown: The $q$-$\bar{q}$-$g^{\star}$ vertex also involves the SU($3$) matrix element and the Dirac $\gamma_{\mu}$ matrix; triple vertices of $g$'s and $g^{\star}$'s also include the usual SU($3$) structure functions and the momenta factors; and quadruple vertices of $g$'s and $g^{\star}$'s also contain the usual structure function factors as well as the metric tensors $g_{\mu \nu}$. Here, $n$, $m$, and $\ell$ are distinct positive integers ($n \neq m \neq \ell$).
• Figure 2: Dijet diagrams involving KK excitations of the gluons. The indices $i$ and $j$ represent distinct ($i \neq j$) quark flavors.
• Figure 3: The contributions of the virtual exchanges of $g^{\star}$'s to the LHC dijet production cross section, $\sigma_{{}_{\mathit{KK}}} = \sigma - \sigma_{{}_{\mathit{SM}}}$, (top) and the ratio of the KK contribution to the SM background, $R = \sigma_{{}_{\mathit{KK}}} / \sigma_{{}_{\mathit{SM}}}$, (bottom) are illustrated as a function of the minimum transverse momentum $p_{{}_T}^{{}^{\mathit{min}}}$ for fixed values of the compactification scale $\mu$. The solid horizontal line represents $\sim 200$ events/yr at the projected integrated luminosity. Discernible bumps in regions for which $p_{{}_T}^{{}^{\mathit{min}}} = k \mu / 2$ are indicated by the corresponding value of $k \in \{1,2,\ldots\}$.
• Figure 4: Same as Fig. \ref{['fig:gs2a']}, but as a function of the compactification scale $\mu$ for fixed values of the minimum transverse momentum $p_{{}_T}^{{}^{\mathit{min}}}$. The horizontal dashed lines represent the SM background.
• Figure 5: The partial contributions to the total dijet cross section are shown as a function of $p_{{}_T}^{{}^{\mathit{min}}}$, for $\mu = 3.5$ TeV.