We determine quark mass dependent order a improvement terms of the form bJam for non-singlet scalar, pseudoscalar, vector and axialvector currents using correlators in coordinate space on a set of CLS ensembles. These have been generated employing non-perturbatively improved Wilson Fermions and the tree-level L\"uscher-Weisz gauge action at β=3.4,3.46,3.55 and 3.7, corresponding to lattice spacings ranging from a≈0.085 fm down to 0.05 fm. In the Nf=2+1 flavour theory two types of improvement coefficients exist: bJ, proportional to non-singlet quark mass combinations, and bˉJ (or b~J), proportional to the trace of the quark mass matrix. Combining our non-perturbative determinations with perturbative results, we quote Pad\'e approximants parameterizing the bJ improvement coefficients within the above window of lattice spacings. We also give preliminary results for b~J at β=3.4.
@article{arxiv.1607.07090,
title = {Non-perturbative determination of improvement coefficients using coordinate space correlators in $N_f=2+1$ lattice QCD},
author = {Piotr Korcyl and Gunnar S. Bali},
journal= {arXiv preprint arXiv:1607.07090},
year = {2017}
}