Physical and cut-off effects of heavy sea quarks

We simulate a theory with two dynamical O($a$) improved Wilson quarks whose mass $M$ ranges from a factor eight up to a factor two below the charm quark mass and at three values of the lattice spacing ranging from 0.066 to 0.034 fm. This theory is a prototype to study the decoupling of heavy quarks. We measure the mass and cut-off dependence of ratios of gluonic observables defined from the Wilson flow or the static potential. The size of the 1/$M$ corrections can be determined and disentangled from the lattice artifacts. The difference with the pure gauge theory is at the percent level when two quarks with a mass of the charm quark are present.