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 f[rom pdg files][1] 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"gnuplot> replot 2.4952*(x/91.1876)**3
      replot 2.99591E-19*(x/0.105658)**5

And you can appreciate the scaling as the blue line here in the log log plot

[![a][2]][2]

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?


  [1]: https://pdg.lbl.gov/2020/html/computer_read.html
  [2]: https://i.sstatic.net/pXYE8.png