The Z boson a_T distribution at hadron colliders

We provide a theoretical study of a novel variable introduced in Ref. \cite{WV} to study the transverse momentum of the Z boson at hadron colliders. The variable we consider has experimental advantages over the standard $p_T$ distribution enabling more accurate measurement at low $p_T$. We provide an all orders perturbative estimate for this variable at the next-to--leading logarithmic accuracy and compare the results to those for the standard $p_T$ distribution. We test our resummation, at the two-loop level, by comparing its expansion to fixed-order perturbative estimates and find agreement with our expectations.