Vacuum expectation value of A^2 from LQCD

We argue from LQCD that there is a non vanishing v.e.v of $A_a^{\mu }{A}_{\mu }^a$ in QCD in the Landau gauge. We use operator product expansion to provide a clear definition of $A_a^{\mu }{A}_{\mu }^a$ and extract a number both in the quenched and unquenched case.