  A search for the production of heavy partners of the top quark with charge
5/3 is performed in events with a pair of same-sign leptons. The data sample
corresponds to an integrated luminosity of 19.5 inverse femtobarns and was
collected at sqrt(s) = 8 TeV by the CMS experiment. No significant excess is
observed in the data above the expected background and the existence of
top-quark partners with masses below 800 GeV is excluded at a 95% confidence
level, assuming they decay exclusively to tW. This is the first limit on these
particles from the LHC, and it is significantly more restrictive than previous
limits.
