$\ge 4 μ$ signal from a vector-like lepton decaying to a muon-philic $Z^\prime$ boson at the LHC

Abstract

We propose a novel possibility to detect a very distinctive signal with more than four muons originating from pair-produced vector-like leptons decaying to a muon-philic Z boson. These new particles are good candidates to explain the anomalies in the muon anomalous magnetic moment and the b → s processes. The doublet (singlet) vector-like leptons lighter than 1.3 (1.0) TeV are excluded by the latest data at the LHC if BR(E → Z µ) = 1. We also show that the excess in the signal region with more than five leptons can be explained by this scenario if the vector-like lepton is a weak singlet, with mass about 400 GeV and BR(E → Z µ) = 0.25. The future prospects at the HL-LHC are discussed.

Challenges for the 3-3-1 models

“…5. In the model with β = − √ 3 with heavy charged leptons E ± l (which are vector-like under the SM symmetries) the production of four muons induced by the Z in pp collisions are possible [128]. In the model with β = −1/ √ 3 there are neutral vectorlike leptons N l , and also this sort of processes are also produced.…”

Complete vectorlike fourth family and new U(1)$^\prime$ for muon anomalies

“…We propose a novel possibility to search for the VL leptons and Z boson [6]. We consider the pair production of VL leptons decaying to a Z boson followed by the Z boson decaying to a pair of muons or muon neutrinos.…”

Fermiophobic $Z'$ model for simultaneously explaining the muon anomalies $R_{K^{(*)}}$ and $(g-2)_μ$

“…a result 4.2σ greater than the SM prediction and in excellent agreement with the previous BNL E821 measurement. Such a discrepancy can also be addressed by Z models [58][59][60][61][62][63][64][65][66] or leptoquarks [67][68][69], along with models involving extended scalar content and/or vector-like (VL) fermions [70][71][72][73]. In particular, the minimal Z explanations [58] require to introduce τ − µ mixing in order to obtain an enhanced contribution proportional to m τ , along with dangerous contributions to the flavour-violating process τ → 3µ, unless further model building is considered.…”

“…The latter is the case of Refs. [59][60][61][62][63][64][65][66], which consider a fermiophobic Z model where the Z couplings with SM fermions are obtained through mixing with a 4th VL family. An enhanced contribution to ∆a µ is obtained through a coupling between the SM Higgs and a 4th VL lepton, although it has to be checked that such a coupling would not spoil the existing Higgs diphoton decay data.…”

“…Refs. [64][65][66] consider our same model but with more general mixing between VL and SM fermions, which also implies a higher number of parameters. Instead, we consider in this article the minimal mixing framework required to explain R K ( * ) and (g − 2) µ simultaneously, where the 4th VL family only mixes with the third generation of the SM quark doublet and with the second generation of the SM lepton doublet and singlet, hence the number of mixing parameters is only three and the parameter space is easier to explore.…”