  A search for the production of heavy partners of the top quark with charge
5/3 (X[5/3]) decaying into a top quark and a W boson is performed with a data
sample corresponding to an integrated luminosity of 2.3 inverse femtobarns,
collected in proton-proton collisions at a center-of-mass energy of 13 TeV with
the CMS detector at the CERN LHC. Final states with either a pair of same-sign
leptons or a single lepton, along with jets, are considered. No significant
excess is observed in the data above the expected standard model background
contribution and an X[5/3] quark with right-handed (left-handed) couplings is
excluded at 95% confidence level for masses below 1020 (990) GeV. These are the
first limits based on a combination of the same-sign dilepton and the
single-lepton final states, as well as the most stringent limits on the X[5/3]
mass to date.
