Discrimination of Supersymmetry and Universal Extra Dimensions at Hadron Colliders

TL;DR

The paper tackles the problem of distinguishing SUSY from Universal Extra Dimensions at hadron colliders by focusing on two robust discriminators: the presence of an extended KK tower (including level-2 states) and spin correlations in cascade decays. It analyzes the production and decay of level-2 KK states, especially the narrow resonances $\gamma_2$ and $Z_2$, and assesses the LHC/Tevatron reach for these states. The study finds that the LHC can discover $\gamma_2$ and $Z_2$ up to $R^{-1}\sim 1~\mathrm{TeV}$, with the potential to resolve the two resonances in dilepton channels, while spin-based discrimination via Barr’s asymmetry is inconclusive in general. The results underscore the importance of higher KK states and resonance structure as model-light handles to distinguish UED from SUSY, while highlighting the need to consider non-minimal UED scenarios and alternative spin observables for robust discrimination.

Abstract

We contrast the experimental signatures of low energy supersymmetry and the model of Universal Extra Dimensions and discuss various methods for their discrimination at hadron colliders. We study the discovery reach of the Tevatron and the LHC for level 2 Kaluza-Klein modes, which would indicate the presence of extra dimensions. We find that with 100 ${\rm fb}^{-1}$ of data the LHC will be able to discover the $γ_2$ and $Z_2$ KK modes as separate resonances if their masses are below 2 TeV. We also investigate the possibility to differentiate the spins of the superpartners and KK modes by means of the asymmetry method of Barr.

Figures (12)

• Figure 1: One-loop corrected mass spectrum of the $n=1$ and $n=2$ KK levels in Minimal UED, for $R^{-1}=500$ GeV, $\Lambda R=20$ and $m_h=120$ GeV. We show the KK modes of gauge bosons, Higgs and Goldstone bosons and first generation fermions.
• Figure 2: Strong production of $n=2$ KK particles at the LHC: (a) KK-quark pair production; (b) KK-quark/KK-gluon associated production and KK-gluon pair production. The cross-sections have been summed over all quark flavors and also include charge-conjugated contributions such as $Q_2\bar{q}_2$, $\bar{Q}_2q_2$, $g_2\bar{Q}_2$, etc.
• Figure 3: Branching fractions of the level 2 "up" quarks versus $R^{-1}$; for (a) the $SU(2)_W$-doublet quark $U_2$ and (b) the $SU(2)_W$-singlet quark $u_2$.
• Figure 4: The same as Fig. \ref{['fig:br_q2']} but for the level 2 KK electrons: (a) the $SU(2)_W$-doublet $E_2$ and (b) the $SU(2)_W$-singlet $e_2$.
• Figure 5: (a) Masses of the four $n=2$ KK gauge bosons as a function of $R^{-1}$. (b) Total widths of the $n=2$ KK gauge bosons as a function of the corresponding mass. We also show the width of a generic $Z'$ whose couplings to the SM particles are the same as those of the $Z$-boson.