  A search for supersymmetry through the direct pair production of top squarks,
with Higgs (H) or Z bosons in the decay chain, is performed using a data sample
of proton-proton collisions at sqrt(s) = 8 TeV collected in 2012 with the CMS
detector at the LHC. The sample corresponds to an integrated luminosity of 19.5
inverse femtobarns. The search is performed using a selection of events
containing leptons and bottom-quark jets. No evidence for a significant excess
of events over the standard model background prediction is observed. The
results are interpreted in the context of simplified supersymmetric models with
pair production of a heavier top-squark mass eigenstate stop[2] decaying to a
lighter top-squark mass eigenstate stop[1] via either stop[2] to H stop[1] or
stop[2] to Z stop[1], followed in both cases by stop[1] to t neutralino, where
neutralino is an undetected, stable, lightest supersymmetric particle. The
interpretation is performed in the region where the mass difference between the
stop[1] and neutralino states is approximately equal to the top-quark mass
(m[stop[1]] - m[neutralino] ~= m[t]), which is not probed by searches for
direct stop[1] squark pair production. The analysis excludes top squarks with
masses m[stop[2]] < 575 GeV and m[stop[1]] < 400 GeV at a 95% confidence level.
