Interpretation of Angular Distributions of $Z$-boson Production at Colliders

Understand

High precision data of dilepton angular distributions in $\gamma^*/Z$ production were reported recently by the CMS Collaboration covering a broad range of the dilepton transverse momentum, $q_T$, up to $\sim 300$ GeV.

• Pronounced $q_T$ dependencies of the $\lambda$ and $\nu$ parameters, characterizing the $\cos^2\theta$ and $\cos 2\phi$ angular distributions, were found.
• Violation of the Lam-Tung relation was also clearly observed.
• We show that the $q_T$ dependence of $\lambda$ allows a determination of the relative contributions of the $q \bar q$ annihilation versus the $qG$ Compton process.