Studies of $\mathrm{Z} \to 4\ell$ decays in proton-proton collisions \\ at $\sqrt{s} = 8$ and $13~\mathrm{TeV}$

Decays of ${\mathrm{Z}}$ bosons to four charged leptons (electrons and muons) are studied in proton-proton collisions at $\sqrt{s} = 8$ and $13~\mathrm{TeV}$. The analysis is based on data collected with the CMS detector at the LHC corresponding to an integrated luminosity of $19.7~\mathrm{fb}^{-1}$ at $8~\mathrm{TeV}$ and $138~\mathrm{fb}^{-1}$ at $13~\mathrm{TeV}$. The measured value of the inclusive branching fraction for all four-lepton decay modes, $\mathcal{B}(\mathrm{Z} \rightarrow 4\ell)$, is $(4.67 \pm 0.11\,(\mathrm{stat})\pm 0.10\,(\mathrm{sys}) ) \times 10^{-6} $ which has a precision of about $3\%$. Measurements of the individual branching fractions for the decays $\mathrm{Z} \rightarrow 4\mu$, $\mathrm{Z} \rightarrow 4\mathrm{e}$, and $\mathrm{Z} \rightarrow 2\mu2\mathrm{e}$ are also reported. Differential decay rates as functions of kinematic and angular quantities in the $\mathrm{Z}$ boson rest frame are presented. Measurements of triple-product asymmetries, which are sensitive to violations of charge conjugation and parity ($\mathit{CP}$) invariance, are performed for $\mathrm{Z} \to 4\ell$ decays. The results are compared to standard model predictions and used to set limits on the production of new gauge bosons.