  We consider a model where the standard model is extended by the addition of a
vector-like isosinglet down-type quark b'. We perform a chi square fit to the
flavor physics data and obtain the preferred central values along with errors
of all the elements of the measurable 3 X 4 quark mixing matrix. The fit
indicates that all the new-physics parameters are consistent with zero and the
mixing of the b' quark with the other three is constrained to be small. The
current flavor physics data rules out possibility of detectable new physics
signals in most of the flavor physics observables. We also investigate possible
deviations in the standard model Wtb couplings and bottom quark coupling to
Higgs boson. We find that these deviations are less than a percent level which
is too small to be observed at the LHC with current precision.
