Abstract
We analyze signals at the Large Hadron Collider (LHC) from production and decay of Kaluza-Klein (KK) gravitons in the context of “extended” warped extra-dimensional models, where the standard model (SM) Higgs and fermion fields are restricted to be in-between the usual ultraviolet/Planck brane and a ∼ O(10) TeV (new, “intermediate”) brane, whereas the SM gauge fields (and gravity) propagate further down to the ∼ O(TeV) infrared brane. Such a framework suppresses flavor violation stemming from KK particle effects, while keeping the KK gauge bosons and gravitons accessible to the LHC. We find that the signals from KK graviton are significantly different than in the standard warped model. This is because the usually dominant decay modes of KK gravitons into top quark, Higgs and longitudinal W/Z particles are suppressed by the above spatial separation between these two sets of particles, thus other decay channels are allowed to shine themselves. In particular, we focus on two novel decay channels of the KK graviton. The first one is the decay into a pair of radions, each of which decays (dominantly) into a pair of SM gluons, resulting in a resonant 4-jet final state consisting of two pairs of dijet resonance. On the other hand, if the radion is heavier and/or KK gluon is lighter, then the KK graviton mostly decays into a KK gluon and a SM gluon. The resulting KK gluon has a significant decay branching fraction into radion and SM gluon, thereby generating (again) a 4-jet signature, but with a different underlying event topology, i.e., featuring now three different resonances. We demonstrate that the High-Luminosity LHC (HL-LHC) has sensitivity to KK graviton of (up to) ∼ 4 TeV in both channels, in the specific model with only gluon field (and gravity) propagating in the extended bulk, whereas it is unlikely to have sensitivity in the standard dijet resonance search channel from KK graviton decay into two gluons.
Highlights
M (4 j)[TeV] M 2 j [TeV]Distribution based on eq (4.4)cos2θ*φ the associated signal feature while substantially rejecting background events
Having outlined the plan of our analysis, we present the results for Large Hadron Collider (LHC) signals arising from production and subsequent decay of KK graviton
We have analyzed signals at the LHC from the production and decay of KK graviton in the framework where the standard model (SM) gauge fields propagate in an extended warped extra dimension
Summary
The model associated with our signal processes has already been outlined in the introductory section [see figure 1(b)] and has been discussed in detail in the theory and phenomenology refs. [17, 23,24,25], so we shall only provide a brief description here. The new particles in this model are the Kaluza-Klein excitations of SM fields, (the lightest ones of) which are localized near the respective “IR” branes, i.e., KK fermions at the Higgs brane and KK gauge/graviton near the final IR brane. As already indicated in the introduction, we focus here on the following two sets of signals stemming from production of KK graviton (denoted by GKK) involving decays into KK gluon (gKK) and/or radion (φ): see figures 1(a) and 1(b). Where KK graviton coupling is denoted by ggrav and m(KAK) stands for the mass of the associated KK gauge boson. The KK gauge boson-SM gauge bosonradion coupling arises after radius stabilization, depends on ∼ ln m(KfK) denoting the KK fermion mass (roughly the scale of Higgs brane). 2 m(KGK) , 10π where coefficients a, b, and c are set to be unity for simplicity
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