  We simulate a theory with $N_f=2$ heavy quarks of mass $M$. At energies much
smaller than $M$ the heavy quarks decouple and the theory can be described by
an effective theory which is a pure gauge theory to leading order in $1/M$. We
present results for the mass dependence of ratios such as $t_0(M)/t_0(0)$. We
compute these ratios from simulations and compare them to the perturbative
prediction. The latter relies on a factorisation formula for the ratios which
is valid to leading order in $1/M$.

High Energy Physics - Lattice;High Energy Physics - Phenomenology