Four-lepton production in proton–proton collisions, pp→(Z/γ⁎)(Z/γ⁎)→l+l−l′+l′−pp→(Z/γ⁎)(Z/γ⁎)→l+l−l′+l′−, where l,l′=el,l′=e or μ, is studied at a center-of-mass energy of 13 TeV with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 2.6 fb−1. The ZZ production cross section, View the MathML sourceσ(pp→ZZ)=14.6−1.8+1.9(stat)−0.3+0.5(syst)±0.2(theo)±0.4(lumi)pb, is measured for events with two opposite-sign, same-flavor lepton pairs produced in the mass region 60<ml+l−,ml′+l′−<120 GeV60<ml+l−,ml′+l′−<120 GeV. The Z boson branching fraction to four leptons is measured to be View the MathML sourceB(Z→l+l−l′+l′−)=4.9−0.7+0.8 (stat)−0.2+0.3 (syst)−0.1+0.2(theo)±0.1(lumi)×10−6 for the four-lepton invariant mass in the range 80<ml+l−l′+l′−<100 GeV80<ml+l−l′+l′−<100 GeV and dilepton mass ml+l−>4 GeVml+l−>4 GeV for all opposite-sign, same-flavor lepton pairs. The results are in agreement with standard model predictions.
