  We present the results of a new study of mass segregation in two-component
star clusters, based on a large number of numerical N-body simulations using
our recently developed dynamical Monte Carlo code. Specifically, we follow the
dynamical evolution of clusters containing stars with individual masses m_1 as
well as a tracer population of objects with individual masses m_2=\mu m_1,
using N=10^5 total stars. For heavy tracers, which could represent stellar
remnants such as neutron stars or black holes in a globular cluster, we
characterize in a variety of ways the tendency for these objects to concentrate
in or near the cluster core. In agreement with simple theoretical arguments, we
find that the characteristic time for this mass segregation process varies as
1/\mu. For models with very light tracers (\mu <~ 10^-2), which could represent
free-floating planets or brown dwarfs, we find the expected depletion of light
objects in the cluster core, but also sometimes a significant enhancement in
the halo. Using these results we estimate the optical depth to gravitational
microlensing by planetary mass objects or brown dwarfs in typical globular
clusters. For some initial conditions, the optical depth in the halo due to
very low-mass objects could be much greater than that of luminous stars. If we
apply our results to M22, using the recent null detection of Sahu, Anderson, &
King (2001), we find an upper limit of ~25% at the 63% confidence level for the
current mass fraction of M22 in the form of very low-mass objects.
