  How do dust grains in protoplanetary disks overcome rapid radial drift and
grow from micron size particles to planets is not well understood. The key is
to search for evidence of dust accumulation and growth as a function of radius
in the disk. We investigate the radial profile of grain size in the DS Tau disk
by fitting multi-band ALMA observations with self-consistent radiative transfer
models. The best-fit grain sizes range from centimeters in the inner disk down
to 30 micron in the outer regions. Such an inside-out decreasing tendency is
consistent with theories of dust evolution. Based on the best-fit model, we
find that dust of 2 Jupiter masses has been depleted within the gap. By taking
the gas-to-dust mass ratio into account, the lost mass is enough to form the
3.5 Jupiter mass planet inferred by literature hydrodynamic simulations.
Moreover, our modeling also indicates that at the interface region between the
gap and the ring, the grain size profile shows a discontinuity, with its
amplitude dependent on the dust model adopted in the radiative transfer
analysis. Future multi-wavelength observations at higher angular resolutions
are required to better constrain the grain size and its variation in the
vicinity of disk substructures.
