  SU(2) gauge theory with Nf=24 massless fermions is non-interacting at long
distances, i.e. it has an infrared fixed point at vanishing coupling. With
massive fermions the fermions are expected to decouple at energy scales below
the fermion mass, and the infrared behaviour is that of confining SU(2) pure
gauge theory. We demonstrate this behaviour non-perturbatively with lattice
Monte Carlo simulations by measuring the gradient flow running coupling.
