Indirect Collider Signals for Extra Dimensions

Abstract

A recent suggestion that quantum gravity may become strong near the weak scale has several testable consequences. In addition to probing for the new large (submillimeter) extra dimensions associated with these theories via gravitational experiments, one could search for the Kaluza Klein towers of massive gravitons which are predicted in these models and which can interact with the fields of the Standard Model. Here we examine the indirect effects of these massive gravitons being exchanged in fermion pair production in \epem annihilation and Drell-Yan production at hadron colliders. In the latter case, we examine a novel feature of this theory, which is the contribution of gluon gluon initiated processes to lepton pair production. We find that these processes provide strong bounds, up to several TeV, on the string scale which are essentially independent of the number of extra dimensions. In addition, we analyze the angular distributions for fermion pair production with spin-2 graviton exchanges and demonstrate that they provide a smoking gun signal for low-scale quantum gravity which cannot be mimicked by other new physics scenarios.

Figures (4)

• Figure 1: Bin integrated angular distribution and $z$-dependent Left-Right asymmetry for $e+e^-$e^+e^-$\rightarrow \mu^+\mu^-\,, b\bar{b}\,, c\bar{c}$. In each case, the solid histogram represents the SM, while the 'data' points are for $M_s=1.5$ TeV with $\lambda=\pm 1$. The error bars correspond to the statistics in each bin.
• Figure 2: Left: 95% C.L. search reach for the string scale as a function of integrated luminosity at ^+e^- $e^+e^-$ colliders with center-of-mass energy as labeled. Right: The percentage confidence level as a function of the string scale for a fit to the 'data' of Fig. \ref{['edists']} assuming the angular distributions take the form expected in the case of new gauge boson exchange. The assumed center-of-mass energy and luminosity is as labeled, and the dashed and solid curves in each case correspond to the choice $\pm\lambda$.
• Figure 3: Bin integrated lepton pair invariant mass distribution and forward-backward asymmetry for Drell-Yan production at the Main Injector and the LHC. The SM is represented by the solid histogram. The data points represent graviton exchanges with (a) $M_s=800$ GeV and $\lambda=+1$ or $-1$, (b) $M_s=800$ GeV and $\lambda=+1$ and $-1$, (c) $M_s=2.5$ and 4.0 TeV and $\lambda=+1$ or $-1$, (d) $M_s=2.5$ TeV and $\lambda=+1$ and $-1$.
• Figure 4: 95% C.L. search reach for the string scale as a function of integrated luminosity at the (a) Tevatron with the sign of $\lambda$ as labeled and (b) LHC for either sign.