QCD predictions for new variables to study dilepton transverse momenta   at hadron colliders
  The D0 collaboration has recently introduced new variables, a_T and phi* to more accurately probe the low Q_T domain of Z boson production at hadron colliders than had been previously possible through a direct study of the Q_T distribution. The comparison of such accurate data to precise theoretical predictions from QCD perturbation theory will yield important information on the ability of resummed QCD predictions as well as parton shower models to describe the low Q_T domain and should enable more stringent constraints on non-perturbative effects. In the present paper we provide analytical predictions for the above mentioned variables, that contain resummation of large logarithms, including next-to-next-to leading logarithmic (NNLL) terms, supplemented by exact next-to-leading order calculations from MCFM. 
Andrea Banfi, Mrinal Dasgupta and Simone Marzani
hep-ph