Speaker
Jen-Chieh Peng
Description
High precision data of dilepton angular distributions in γ∗/Z production were reported recently by the CMS Collaboration covering a broad range of the dilepton transverse momentum, qT , up to _ 300 GeV. Pronounced qT dependencies of the λ and ν parameters, characterizing the cos2 θ and cos 2φ angular distributions, were found. Violation of the Lam-Tung relation was also clearly observed. We show that the qT dependence of λ allows a determination of the relative contributions of the q¯q annihilation versus the qG Compton process. The violation of the Lam-Tung relation is attributed to the presence of a non-zero component of the q − ¯q axis in the direction normal to the “hadron plane” formed by the colliding hadrons. The observed qT dependencies of λ and ν from the CMS and the earlier CDF data can be well described using this approach.
