  We compute the time-resolved photoemission spectrum after photo-doping in a
two-dimensional Mott-Hubbard insulator. We find that the relaxation rate of
high-energy photo-doped electrons in the paramagnetic phase scales with the
strength of the nearest-neighbor spin correlations, which implies a pronounced
increase of the relaxation times with temperature and excitation density.
Finite doping, in contrast, opens additional scattering channels and leads to a
faster relaxation. To obtain our results we have implemented a nonequilibrium
version of the dynamical cluster approximation (DCA), which, in contrast to
single-site dynamical mean-field theory, captures the effect of short-range
correlations.
