  Measurements of the cross sections for top quark pairs produced in
association with a W or Z boson are presented, using 8 TeV pp collision data
corresponding to an integrated luminosity of 19.5 inverse femtobarns, collected
by the CMS experiment at the LHC. Final states are selected in which the
associated W boson decays to a charged lepton and a neutrino or the Z boson
decays to two charged leptons. Signal events are identified by matching
reconstructed objects in the detector to specific final state particles from
ttW or ttZ decays. The ttW cross section is measured to be 382 +117 -102 fb
with a significance of 4.8 standard deviations from the background-only
hypothesis. The ttZ cross section is measured to be 242 +65 -55 fb with a
significance of 6.4 standard deviations from the background-only hypothesis.
These measurements are used to set bounds on five anomalous dimension-six
operators that would affect the ttW and ttZ cross sections.
