  The NASA/DART (Double Asteroid Redirection Test) spacecraft successfully
crashed on Dimorphos, the secondary component of the binary (65803) Didymos
system. Following the impact, a large dust cloud was released, and a
long-lasting dust tail was developed. We have extensively monitored the dust
tail from the ground and from the Hubble Space Telescope (HST). We provide a
characterization of the ejecta dust properties, i.e., particle size
distribution and ejection speeds, ejection geometric parameters, and mass, by
combining both observational data sets, and by using Monte Carlo models of the
observed dust tail. The differential size distribution function that best fits
the imaging data was a broken power-law, having a power index of --2.5 for
particles of r$\le$ 3 mm, and of --3.7 for larger particles. The particles
range in sizes from 1 $\mu$m up to 5 cm. The ejecta is characterized by two
components, depending on velocity and ejection direction. The northern
component of the double tail, observed since October 8th 2022, might be
associated to a secondary ejection event from impacting debris on Didymos,
although it is also possible that this feature results from the binary system
dynamics alone. The lower limit to the total dust mass ejected is estimated at
$\sim$6$\times$10$^6$ kg, half of this mass being ejected to interplanetary
space.
