  We obtain the exact time evolution for the one-dimensional integrable
fermionic 1/r Hubbard model after a sudden change of its interaction parameter,
starting from either a metallic or a Mott-insulating eigenstate. In all cases
the system relaxes to a new steady state, showing that the presence of the Mott
gap does not inhibit relaxation. The properties of the final state are
described by a generalized Gibbs ensemble. We discuss under which conditions
such ensembles provide the correct statistical description of isolated
integrable systems in general. We find that generalized Gibbs ensembles do
predict the properties of the steady state correctly, provided that the
observables or initial states are sufficiently uncorrelated in terms of the
constants of motion.
