Search for charged lepton flavor violating $ Z$ and $ {Z}^{\prime }$ boson decays in proton-proton collisions at $ \sqrt{s}=13\text{}\text{}\mathrm{TeV}$

A search for flavor violating decays of the $ Z$ boson to charged leptons is performed using data from proton-proton collisions at $ \sqrt{s}=13\text{}\text{}\mathrm{TeV}$ collected with the CMS detector at the LHC, corresponding to an integrated luminosity of $ 138\text{}\text{}{\mathrm{fb}}^{-1}$. Each of the decays $ Z\to e\mu $, $ Z\to e\tau $, and $ Z\to \mu \tau $ is considered. The data are consistent with the backgrounds expected from standard model processes. For the $ Z\to e\mu $ channel the observed (expected) 95% confidence level upper limit on the branching fraction is $ 1.9(2.0)\times {10}^{-7}$, which is the most stringent direct limit to date on this process; the corresponding limits for the $ Z\to e\tau $ and $ Z\to \mu \tau $ channels are $ 13.8(11.4)\times {10}^{-6}$ and $ 12.0(5.3)\times {10}^{-6}$, respectively. Additionally, the $ e\mu $ final state is used to search for lepton flavor violating decays of $ {Z}^{\prime }$ resonances in the mass range from 110 to $ 500\text{}\text{}\mathrm{GeV}$. No significant excess is observed above the predicted background levels.