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Register a new userSignals of Two Universal Extra Dimensions at the LHC
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Extensions of the standard model with universal extra dimensions are interesting both as phenomenological templates as well as model-building fertile ground. For instance, they are one the prototypes for theories exhibiting compressed spectra, leading to difficult searches at the LHC since the decay products of new states are soft and immersed in a large standard model background. Here we study the phenomenology at the LHC of theories with two universal extra dimensions. We obtain the current bound by using the production of second level excitations of electroweak gauge bosons decaying to a pair of leptons and study the reach of the LHC Run~II in this channel. We also introduce a new channel originating in higher dimensional operators and resulting in the single production of a second level quark excitation. Its subsequent decay into a hard jet and lepton pair resonance would allow the identification of a more model-specific process, unlike the more generic vector resonance signal. We show that the sensitivity of this channel to the compactification scale is very similar to the one obtained using the vector resonance.
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The usual universal extra dimensions scenario does not allow for single production of first level Kaluza-Klein (KK) excitations of matter due to the KK number conservation. However, if the matter fields are localized on a fat brane embedded in a higher dimensional space, matter-gravitation interactions violate KK number, and the production of single KK excitations becomes possible. In this paper we analyze the production of a single KK matter excitation together with a graviton in the final state, and study the potential for discovery at the Tevatron and Large Hadron Collider.
Universal extra dimensions and supersymmetry have rather similar experimental signatures at hadron colliders. The proper interpretation of an LHC discovery in either case may therefore require further data from a lepton collider. In this paper we identify methods for discriminating between the two scenarios at the linear collider. We study the processes of Kaluza-Klein muon pair production in universal extra dimensions in parallel to smuon pair production in supersymmetry, accounting for the effects of detector resolution, beam-beam interactions and accelerator induced backgrounds. We find that the angular distributions of the final state muons, the energy spectrum of the radiative return photon and the total cross-section measurement are powerful discriminators between the two models. Accurate determination of the particle masses can be obtained both by a study of the momentum spectrum of the final state leptons and by a scan of the particle pair production thresholds. We also calculate the production rates of various Kaluza-Klein particles and discuss the associated signatures.
Theories with extra dimensions of inverse TeV size (or larger) predict a multitude of signals which can be searched for at present and future colliders. In this paper, we review the different phenomenological signatures of a particular class of models, universal extra dimensions, where all matter fields propagate in the bulk. Such models have interesting features, in particular Kaluza-Klein (KK) number conservation, which makes their phenomenology similar to that of supersymmetric theories. Thus, KK excitations of matter are produced in pairs, and decay to a lightest KK particle (LKP), which is stable and weakly interacting, and therefore will appear as missing energy in the detector (similar to a neutralino LSP). Adding gravitational interactions which can break KK number conservation greatly expands the class of possible signatures. Thus, if gravity is the primary cause for the decay of KK excitations of matter, the experimental signals at hadron colliders will be jets + missing energy, which is typical of supergravity models. If the KK quarks and gluons decay first to the LKP, which then decays gravitationally, the experimental signal will be photons and/or leptons (with some jets), which resembles the phenomenology of gauge mediated supersymmetry breaking models.
I extract new limits on the coefficient of the effective operator generated by tree-level graviton exchange in large extra dimensions from $pp rightarrow jj$ angular distributions at LHC: $M_T > 6.8$ TeV (CMS after $2.6 fb^{-1}$ of integrated luminosity) and $M_T > 8.3$ TeV (ATLAS after $3.6 fb^{-1}$). I also compare such limits to the ones obtained using the full graviton amplitude, and discuss the impact of additional constrains arising from other datasets, such as Mono-Jet.
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 and lepton colliders. We study the discovery reach of hadron colliders for level 2 Kaluza-Klein modes, which would indicate the presence of extra dimensions. We also investigate the possibility to differentiate the spins of the superpartners and KK modes by means of the asymmetry method of Barr. We then review the methods for discriminating between the two scenarios at a high energy linear collider such as CLIC. We consider the processes of Kaluza-Klein muon pair production in universal extra dimensions in parallel to smuon pair production in supersymmetry. We find that the angular distributions of the final state muons, the energy spectrum of the radiative return photon and the total cross-section measurement are powerful discriminators between the two models.
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