  A relation between the mass accretion rate onto the central young star and
the mass of the surrounding protoplanetary disk has long been theoretically
predicted and observationally sought. For the first time, we have accurately
and homogeneously determined the photospheric parameters, mass accretion rate,
and disk mass for an essentially complete sample of young stars with disks in
the Lupus clouds. Our work combines the results of surveys conducted with
VLT/X-Shooter and ALMA. With this dataset we are able to test a basic
prediction of viscous accretion theory, the existence of a linear relation
between the mass accretion rate onto the central star and the total disk mass.
We find a correlation between the mass accretion rate and the disk dust mass,
with a ratio that is roughly consistent with the expected viscous timescale
when assuming an interstellar medium (ISM) gas-to-dust ratio. This confirms
that mass accretion rates are related to the properties of the outer disk. We
find no correlation between mass accretion rates and the disk mass measured by
CO isotopologues emission lines, possibly owing to the small number of measured
disk gas masses. This suggests that the mm-sized dust mass better traces the
total disk mass and that masses derived from CO may be underestimated, at least
in some cases.
