Speaker
Description
We study the Drell-Yan structure functions in $Z^0$ boson production within the $k_T$ factorization framework, with particular emphasis on the Lam-Tung relation. The NNLO predictions in collinear perturbative QCD underestimate the ATLAS measurement of the Lam-Tung structure function. We investigate impact of parton transverse momenta on description of this observable and the other Drell-Yan structure functions. We take into account the contribution from the scattering of two off-shell gluons and from the scattering of a valence quark and an off-shell gluon, both evaluated at the tree level. Using several gluon transverse momentum dependent distribution (TMD) models, we compute the five non-vanishing Drell-Yan structure functions as a function of the dilepton transverse momentum and compare our results with the ATLAS data. We show that the structure functions strongly discriminate between the TMD models
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