For beta decay of mesons, the heavy quark approximation and surely other techniques can be used to show that the decay width scales as the quintic power of mass. This can be checked from pdg files very easily with this gnuplot script:

  set logscale xy
  set key noautotitle
  plot "<cat Downloads/mass_width_2020.mcd|grep -v ^* | cut -c 32-" using "%20lf%*8lf%*8lf%16lf"
  replot 2.4952*(x/91.1876)**3
  replot 2.99591E-19*(x/0.105658)**5

The plot includes all the particles having mass and decay width listed in the particle data group datafile: mesons and baryons, some of their excited states, and also the Z0 and the W and the two unstable leptons, muon and tau. And the top quark. Higgs boson does not appear because its decay width is not yet in the table, proton does not appear because it is stable AFAWK, and well, the neutron does not appear because I have zoomed it out)

Units in the table are GeV (mass in the horizontal, decay with in the vertical). And you can appreciate the aforementioned quintic scaling as the blue line here.

But surprise, there is also an alignment for neutral, purely electromagnetic, decays. It is a cubic scaling. Is it an artifact, or can it be shown analytically?