Non-perturbative effects in the W and Z transverse momentum distribution
  We use the "dispersive method" to investigate non-perturbative effects in the transverse momentum distribution of vector bosons produced in p-pbar collisions. The assumption of a non-perturbative modification to the running coupling at low scales leads to additional contributions in impact parameter space proportional to -b^2 log Q^2 and -b^2. Our results, which we expect to be valid provided tau is not close to 1, are shown to account for a substantial proportion of the total non-perturbative contribution extracted from data. 
A. Guffanti (Milano), G.E. Smye (Cambridge)