Collider signals of $W'$ and $Z'$ bosons in the gauge-Higgs unification

Abstract

In the $SO(5)\times U(1)$ gauge-Higgs unification (GHU), Kaluza-Klein (KK) excited states of charged and neutral vector bosons, $W^{(1)}$, $W_R^{(1)}$, $Z^{(1)}$, $\gamma^{(1)}$ and $Z_R^{(1)}$, can be observed as $W'$ and $Z'$ signals in collider experiments. In this paper we evaluate the decay rates of the $W'$ and $Z'$, and $s$-channel cross sections mediated by $W'$ and $Z'$ bosons with final states involving the standard model (SM) fermion pair ($\ell \nu$, $\ell\bar{\ell}$, $q\bar{q}'$), $WH$, $ZH$, $WW$ and $WZ$. $W'$ and $Z'$ resonances appear around 6.0 TeV (8.5 TeV) for $\theta_H=0.115$ (0.0737) where $\theta_H$ is the Aharonov-Bohm phase in the fifth dimension in GHU. For decay rates we find $\Gamma(W'\to WH) \simeq \Gamma(W'\to WZ)$ ($W'=W^{(1)}$, $W_R^{(1)}$), $\Gamma(W^{(1)}\to WH,WZ) \sim\Gamma(W_R^{(1)}\to WH,WZ)$, $\Gamma(Z^{(1)}\to ZH) \simeq\sum_{Z'=Z^{(1)},\gamma^{(1)}}\Gamma(Z'\to WW)$, and $\Gamma(Z_R^{(1)}\to ZH) \simeq \Gamma(Z_R^{(1)}\to WW)$. $W'$ and $Z'$ signals of GHU can be best found at the LHC experiment in the processes $pp\to W' (Z')+X$ followed by $W'\to t\bar{b}$, $WH$, and $Z'\to e^+ e^-$, $\mu^+\mu^-, ZH$. For the lighter $Z'$ ($\theta_H = 0.115$) case, with forthcoming 30 fb$^{-1}$ data of the 13 TeV LHC experiment we expect about ten $\mu^+\mu^-$ events for the invariant mass range 3 to 7 TeV, though the number of the events becomes much smaller when $\theta_H=0.0737$. In the process with $WZ$ in the final state, it is confirmed that the unitarity is preserved, provided that all KK excited intermediate states are taken into account. Deviation of the $WWZ$ coupling from the SM is very tiny. Exotic partners $t_T^{(1)}$ and $b_Y^{(1)}$ of the top and bottom quarks with electric charge $+5/3$ and $-4/3$ have mass $M_{t_T^{(1)},b_Y^{(1)}}\simeq 4-5$ TeV, becoming the lightest non-SM particles in GHU which can be singly produced in collider experiments.