Bounds on Universal Extra Dimension from LHC Run I and II data

Abstract

We discuss the collider bounds on minimal Universal Extra Dimension (mUED) model from LHC Run-I and II data. The phenomenology of mUED is determined by only two parameters namely, the compactification scale ($R^{-1}$) of the extra dimension and cutoff scale ($Λ$) of the theory. The characteristic feature of mUED is the occurrence of nearly degenerate mass spectrum for the Kaluza-Klein (KK) particles and hence, soft leptons, soft jets at the collider experiments. The degree of degeneracy of KK-mass spectrum crucially depends on $Λ$. The strongest direct bound on $R^{-1}$ ($\sim $950 GeV for large $Λ$) arises from a search for a pair of soft dimuons at the Large Hadron Collider (LHC) experiment with 8 TeV center-of-mass energy and $20~{\rm fb}^{-1}$ integrated luminosity. However, for small $Λ$ and hence, small splitting within the first KK-level, the bounds from the dimuon channel is rather weak. On the other hand, the discovery of 126 GeV Higgs boson demands small $Λ$ to prevent the scalar potential form being unbounded from below. We discuss LHC monojet searches as a probe of low $Λ$ region of mUED parameter space. We also compute bounds on the mUED parameter space from 13 TeV multijets results.