  A search is presented for a heavy vector-like quark, decaying into a b quark
and a W boson, which is produced singly in association with a light flavor
quark and a b quark. The analysis is performed using a data sample of
proton-proton collisions at a center-of-mass energy of sqrt(s) = 13 TeV
collected at the LHC in 2015. The data set used in the analysis corresponds to
an integrated luminosity of 2.3 inverse femtobarns. The search is carried out
using events containing one electron or muon, at least one b-tagged jet with
large transverse momentum, at least one jet in the forward region of the
detector, and missing transverse momentum. No excess over the standard model
prediction is observed. Upper limits are placed on the production cross section
of heavy exotic quarks: a T quark with a charge of 2/3, and a Y quark with a
charge of -4/3. For Y quarks with coupling of 0.5 and B(Y to bW) = 100%, the
observed (expected) lower mass limits are 1.40 (1.0) TeV. This is the most
stringent limit to date on the single production of the Y vector-like quark.
