The a T distribution of the Z boson at hadron colliders

We provide the first theoretical study of a novel variable, a T, proposed in ref. [1] as a more accurate probe of the region of low transverse momentum p T, for the Z boson p T distribution at hadron colliders. The a T is the component of p T transverse to a suitably defined axis. Our study involves resummation of large logarithms in a T up to the next-to-leading logarithmic accuracy and we compare the results to those for the well-known p T distribution, identifying important physical differences between the two cases. We also test our resummed result at the two-loop level by comparing its expansion to order α s 2 with the corresponding fixed-order results and find agreement with our expectations. © 2009 SISSA.