  A search is performed for long-lived particles that decay into final states
that include a pair of electrons or a pair of muons. The experimental signature
is a distinctive topology consisting of a pair of charged leptons originating
from a displaced secondary vertex. Events corresponding to an integrated
luminosity of 19.6 (20.5) inverse femtobarns in the electron (muon) channel
were collected with the CMS detector at the CERN LHC in proton-proton
collisions at sqrt(s) = 8 TeV. No significant excess is observed above standard
model expectations. Upper limits on the product of the cross section and
branching fraction of such a signal are presented as a function of the
long-lived particle's mean proper decay length. The limits are presented in an
approximately model-independent way, allowing them to be applied to a wide
class of models yielding the above topology. Over much of the investigated
parameter space, the limits obtained are the most stringent to date. In the
specific case of a model in which a Higgs boson in the mass range 125-1000 GeV
decays into a pair of long-lived neutral bosons in the mass range 20-350 GeV,
each of which can then decay to dileptons, the upper limits obtained are
typically in the range 0.2-10 fb for mean proper decay lengths of the
long-lived particles in the range 0.01-100 cm. In the case of the lowest Higgs
mass considered (125 GeV), the limits are in the range 2-50 fb. These limits
are sensitive to Higgs boson branching fractions as low as 1E-4.
