The aT distribution of the Z boson at hadron colliders

We provide the first theoretical study of a novel variable, aT , proposed in Ref. [1] as a more accurate probe of the region of low transverse momentum pT , for the Z boson pT distribution at hadron colliders. The aT is the component of pT transverse to a suitably defined axis. Our study involves resummation of large logarithms in aT up to the next-to–leading logarithmic accuracy and we compare the results to those for the wellknown pT 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 αs with the corresponding fixed-order results and find agreement with our expectations.