  Four-lepton production in proton-proton collisions, pp to
(Z/gamma*)(Z/gamma*) to l+l-l'+l'-, where l, l' = e or mu, 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 inverse femtobarns. The
ZZ production cross section, sigma(pp to 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[l+l-], m[l'+l'-] < 120 GeV. The Z boson branching fraction to four leptons is
measured to be B(Z to l+l-l'+l'-) = 4.9 +0.8/-0.7 (stat) +0.3/-0.2 (syst)
+0.2/-0.1 (theo) +/- 0.1 (lumi) x E-6 for the four-lepton invariant mass in the
range 80 < m[l+l-l'+l'-] < 100 GeV and dilepton mass m[l+l-] > 4 GeV for all
opposite-sign, same-flavor lepton pairs. The results are in agreement with
standard model predictions.
