Measurements of the p p → Z Z production cross section and the Z → 4 ℓ branching fraction, and constraints on anomalous triple gauge couplings at s = 13 TeV

Abstract

Four-lepton production in proton-proton collisions, $pp\to (Z/{\gamma }^{\ast })(Z/{\gamma }^{\ast })\to 4\ell$ , where $\ell =e$ or $\mu$ , is studied at a center-of-mass energy of 13 $\text{TeV}$ with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 35.9 ${\text{fb}}^{-1}$ . The ZZ production cross section, $\sigma (pp\to ZZ)=17.2\pm 0.5\text{(stat)}\pm 0.7\text{(syst)}\pm 0.4\text{(theo)}\pm 0.4\text{(lumi) pb}$ , measured using events with two opposite-sign, same-flavor lepton pairs produced in the mass region $60<m_{{\ell }^{+}{\ell }^{-}}<120\text{GeV}$ , is consistent with standard model predictions. Differential cross sections are measured and are well described by the theoretical predictions. The Z boson branching fraction to four leptons is measured to be $B(Z\to 4\ell )=4.{83}_{-0.22}^{+0.23}{\left(stat\right)}_{-0.29}^{+0.32}\left(syst\right)\pm 0.08\left(theo\right)\pm 0.12\left(lumi\right)\times {10}^{-6}$ for events with a four-lepton invariant mass in the range $80<m_{4\ell }<100\text{GeV}$ and a dilepton mass $m_{\ell \ell }>4\text{GeV}$ for all opposite-sign, same-flavor lepton pairs. The results agree with standard model predictions. The invariant mass distribution of the four-lepton system is used to set limits on anomalous ZZZ and ZZ $\gamma$ couplings at 95% confidence level: $-0.0012<f_4^Z<0.0010$ , $-0.0010<f_5^Z<0.0013$ , $-0.0012<f_4^{\gamma }<0.0013$ , $-0.0012<f_5^{\gamma }<0.0013$ .