W-boson exotic decay into three charged leptons at the LHC

We investigate the W boson's exotic decay channel, W→ℓℓℓν, at the LHC. Although the four-body final states suppress the decay branching ratio, the large production of W bosons makes detecting and precisely measuring this decay probability entirely feasible. Our simulation study indicates that this tiny branching ratio can be measured with subpercent precision at the HL-LHC. This decay channel can also constrain Standard Model extensions. Using the Lμ-Lτ model as a benchmark, we find that the current bound on the gauge coupling for Z′ mass in the range of [4, 75] GeV can significantly improve.