  A measurement of vector boson scattering and constraints on anomalous quartic
gauge couplings from events with two Z bosons and two jets are presented. The
analysis is based on a data sample of proton-proton collisions at sqrt(s) = 13
TeV collected with the CMS detector and corresponding to an integrated
luminosity of 35.9 inverse femtobarns. The search is performed in the fully
leptonic final state ZZ to lll'l', where l, l' = e, mu. The electroweak
production of two Z bosons in association with two jets is measured with an
observed (expected) significance of 2.7 (1.6) standard deviations. A fiducial
cross section for the electroweak production is measured to be sigma[EW](pp ->
ZZjj -> lll'l'jj) = 0.40 -0.16 +0.21 (stat) -0.09 +0.13 (syst) fb, which is
consistent with the standard model prediction. Limits on anomalous quartic
gauge couplings are determined in terms of the effective field theory operators
T0, T1, T2, T8, and T9. This is the first measurement of vector boson
scattering in the ZZ channel at the LHC.
