Search for the Z boson decay to $\tau^+\tau^-\mu^+\mu^-$ in proton-proton collisions at $\sqrt{s}=13\,\text{TeV}$

The first search for the Z boson decay to $\tau^+\tau^-\mu^+\mu^-$ is presented. The data analyzed were collected by the CMS experiment at the CERN LHC in proton-proton collisions at a center-of-mass energy of $13\,\text{TeV}$ and correspond to an integrated luminosity of $138\,\text{fb}^{-1}$. Targeting tau lepton decays to muons and neutrinos, events with two pairs of oppositely charged muons are analyzed. The data are found to be compatible with the predicted background. A $95\%$ confidence level upper limit of 6.2 is placed on the ratio of the ${\text{Z}\to\tau^+\tau^-\mu^+\mu^-}$ to ${\text{Z}\to\mu^+\mu^-\mu^+\mu^-}$ branching fractions, excluding values above 6.9 times the standard model expectation.