Four-lepton production in proton–proton collisions, pp → (Z/γ ∗)(Z/γ ∗) → +−+−, where , = 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, σ(pp → ZZ) =
14.6+1.9
−1.8 (stat) +0.5
−0.3 (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 < m+− ,m+− < 120 GeV. The Z boson branching
fraction to four leptons is measured to be B(Z → +−+−) = 4.9+0.8
−0.7 (stat)+0.3
−0.2 (syst)+0.2
−0.1 (theo) ±
0.1 (lumi)×10−6 for the four-lepton invariant mass in the range 80 < m+−+− < 100 GeV and dilepton
mass m+− > 4 GeV for all opposite-sign, same-flavor lepton pairs. The results are in agreement with
standard model predictions.