  As the classic viscous paradigm for protoplanetary disk accretion is
challenged by the observational evidence of low turbulence, the alternative
scenario of MHD disk winds is being explored as potentially able to reproduce
the same observed features traditionally explained with viscosity. Although the
two models lead to different disk properties, none of them has been ruled out
by observations - mainly due to instrumental limitations. In this work, we
present a viable method to distinguish between the viscous and MHD framework
based on the different evolution of the distribution in the disk mass
($M_{\mathrm{d}}$) - accretion rate ($\dot M$) plane of a disk population. With
a synergy of analytical calculations and 1D numerical simulations, performed
with the population synthesis code \texttt{Diskpop}, we find that both
mechanisms predict the spread of the observed ratio $M_{\mathrm{d}}/\dot M$ in
a disk population to decrease over time; however, this effect is much less
pronounced in MHD-dominated populations as compared to purely viscous
populations. Furthermore, we demonstrate that this difference is detectable
with the current observational facilities: we show that convolving the
intrinsic spread with the observational uncertainties does not affect our
result, as the observed spread in the MHD case remains significantly larger
than in the viscous scenario. While the most recent data available show a
better agreement with the wind model, ongoing and future efforts to obtain
direct gas mass measurements with ALMA and ngVLA will cause a reassessment of
this comparison in the near future.
