LHC Signals for Warped Electroweak Charged Gauge Bosons

TL;DR

This work investigates LHC prospects for the first Kaluza-Klein excitations of electroweak charged gauge bosons in a warped extra-dimension framework with bulk SM fields. It analyzes production via Drell-Yan and multiple decay channels—$t\bar{b}$, $Z W$, and $W h$—including fully leptonic and semi-leptonic final states, and develops jet-mass and boosted-object techniques to distinguish signal from sizable SM and QCD backgrounds. The study finds that $W'$ states with masses around $2$ TeV can be probed with ~100 fb$^{-1}$, while $3$ TeV states require ~300–1000 fb$^{-1}$ depending on the channel and top/bottom sector realization; boosted top, bottom, and Higgs tagging significantly enhances reach. The results are framed in the context of RS1/CFT duality and are argued to be applicable to broader non-supersymmetric EWSB scenarios, underscoring the complementarity of charged EW KK searches with KK gluon and neutral KK searches in a realistic LHC program.

Abstract

We study signals at the Large Hadron Collider (LHC) for the Kaluza-Klein (KK) excitations of electroweak charged gauge bosons in the framework of the Standard Model (SM) fields propagating in the bulk of a warped extra dimension. Such a scenario can solve both the Planck-weak and flavor hierarchy problems of the SM. There are two such charged states in this scenario with couplings to light quarks and leptons being suppressed relative to those in the SM, whereas the couplings to top/bottom quarks are enhanced, similar to the case of electroweak neutral gauge bosons previously studied. However, unlike the case of electroweak neutral gauge bosons, there is no irreducible QCD background (including pollution from possibly degenerate KK gluons) for decays to top + bottom final state so that this channel is useful for the discovery of the charged states. Moreover, decays of electroweak charged gauge bosons to longitudinal W, Z and Higgs are enhanced just as for the neutral bosons. However, unlike for the neutral gauge bosons, the purely leptonic (and hence clean) decay mode of the WZ are fully reconstructible so that the ratio of the signal to the SM (electroweak) background can potentially be enhanced by restricting to the resonance region more efficiently. We show that such final states can give sensitivity to 2 (3) TeV masses with an integrated luminosity of 100 (300) inverse fb. We emphasize that improvements in discriminating a QCD-jet from a highly boosted hadronically decaying W, and a highly boosted top-jet from a bottom-jet will enhance the reach for these KK particles, and that the signals we study for the warped extra dimensional model might actually be applicable also to a wider class of non-supersymmetric models of electroweak symmetry breaking.

Figures (8)

• Figure 1: The total widths of $W'_L$ and $W'_R$ as a function of their masses for cases (i) and (ii).
• Figure 2:
• Figure 3: Total production cross-section for $W'$ versus its mass at the LHC.
• Figure 4: The (a) ${p_T}_t$, and (b) ${M_T}_{tb}$ differential distributions of the process $pp\rightarrow {W^\prime}^+ \rightarrow t \bar{b}$ for $M_{{W^\prime}} = 2$, 3 and 4 TeV for case (i). These are after the cuts in Eq. (\ref{['eq:cutq']}). Also shown are the SM single top background distributions.
• Figure 5: The (a) ${p_T}_W$, (b) ${M_T}_{Wb}$, (c) $\cos_T{\theta_{Wb}}$, and (d) ${M_T}_{Wb\bar{b}}$ differential distributions of the process $pp\rightarrow W^+ b \bar{b}$ for $M_{{W^\prime}} = 2$ TeV, for case (i). Also shown are the irreducible backgrounds, the SM single top $t\bar{b}$ and $W b \bar{b}$.