Measurement of the pp$\rightarrow$ZZ production cross section, $\mathrm{Z} \to 4\ell$ branching fraction and constraints on anomalous triple gauge couplings at $\sqrt{s} = 13~\mathrm{TeV}$

Four-lepton production in proton-proton collisions, $\mathrm{pp} \to (\mathrm{Z} / \gamma^*)(\mathrm{Z}/ \gamma^*) \to 4\ell$, where $\ell, \ell' = \mathrm{e}$ or $\mu$, is studied at a center-of-mass energy of $13~\mathrm{TeV}$ with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of $35.9~\mathrm{fb}^{-1}$. The ZZ production cross section, $\sigma(\mathrm{pp} \to \mathrm{ZZ}) = 17.8 \pm 0.6~(\mathrm{stat})_{-0.6}^{+0.7}~(\mathrm{syst}) \pm 0.4~(\mathrm{theo}) \pm 0.5~\mathrm{lumi})~\mathrm{pb}$, measured for events with two opposite-sign, same-flavor lepton pairs produced in the mass region $60 < m_{\ell^+\ell^-}, m_{\ell^{\prime +}\ell^{\prime -}} < 120~\mathrm{GeV}$ is consistent with standard model predictions. Differential cross sections are measured and well described by the theoretical predictions. The Z boson branching fraction to four leptons is measured to be $\mathcal{B}(\mathrm{Z \to 4\ell}) = 4.74 \pm 0.16~(\mathrm{stat})_{-0.17}^{+0.18}~(\mathrm{syst}) \pm 0.08~(\mathrm{theo}) \pm 0.12~(\mathrm{lumi}) \times 10^{-6}$ for events with four-lepton invariant mass in the range $80 < m_{4\ell} < 100~\mathrm{GeV}$ and dilepton mass $m_{\ell^+\ell^-} > 4~\mathrm{GeV}$ for all opposite-sign, same-flavor lepton pairs. The invariant mass distribution of the four-lepton system is used to set limits on anomalous ZZZ and ZZ$\gamma$ couplings at the $95\%$ confidence level: $-0.00117<f_4^{\mathrm{Z}}<0.00110$, $-0.00100<f_5^{\mathrm{Z}}<0.00125$, $-0.00133<f_4^{\gamma}<0.00132$, and $-0.00123<f_5^{\gamma}<0.00130$. The results agree with standard model predictions.