2025/03/10 by Abu-Ajamieh, Fayez, Ahriche, Amine, Okada, Nobuchika · 2 citations
#FOS: Physical sciences #High Energy Physics - Phenomenology (hep-ph)
paper · doi:10.48550/arxiv.2503.07236
We investigate the experimental bounds on the Flavor-Violating (FV) couplings of the Z boson to the charged leptons. In addition to the direct LHC searches for FV Z decays to leptons, we investigate indirect bounds from flavor-conserving Z decays to leptons at 1-loop, bounds from LEP searches, Electroweak Precision Observables (EWPO), ℓi→ℓjγ decays, ℓi→3ℓj decays, ℓi→ℓj+inv. decays, FV meson decays to leptons, FV τ decays to μ(e) + mesons, muon conversion in nuclei, and from muonium-antimuonium oscillations. For FV Z couplings to τμ, we find that τ→μγ yields the strongest bounds, with a level reaching O(10-5), followed by bounds from τ→3μ(μee). For FV Z couplings to τe, we find that the strongest bounds arise from the decay τ→μμe, reaching O(10-7) as well, with bounds from τ→3e also yielding strong bounds. For FV Z couplings to μe, we find that the strongest bounds are obtained from the decay μ→3e, reaching O(10-11), with bounds from μ→ eγ, muon conversion, KL0→μe and μ→ e+inv. also providing strong bounds. We also study projections from future experiments, such as the FCC-ee, Belle II and the Mu2e experiment. For the Z couplings to τμ, we find that future experiments could improve the bound to O(10-6), whereas for the Z couplings to τe, we find that future experiments could improve the bound to O(10-8), and for the Z couplings to μe, they could improve the bound to O(10-13)