Non-perturbative renormalization of quark bilinear operators with Nf=2 (tmQCD) Wilson fermions and the tree-level improved gauge action

We present results for the renormalization constants of bilinear quark operators obtained by using the tree-level Symanzik improved gauge action and the N-f = 2 twisted mass fermion action at maximal twist, which guarantees automatic O(a)-improvement. Our results are also relevant for the corresponding standard (un-twisted) Wilson fermionic action since the two actions only differ, in the massless limit, by a chiral rotation of the quark fields. The scale-independent renormalization constants Z(V), Z(A) and the ratio Z(P)/Z(S) have been computed using the RI-MOM approach, as well as other alternative methods. For Z(A) and Z(P)/Z(S), the latter are based on both standard twisted mass and Osterwalder-Seiler fermions, while for Z(V) a Ward Identity has been used. The quark field renormalization constant Z(q) and the scale dependent renormalization constants Z(S), Z(P) and Z(T) are determined in the RI-MOM scheme. Leading discretization effects of O(g(2)alpha(2)), evaluated in one-loop perturbation theory, are explicitly subtracted from the RI-MOM estimates.