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

Abstract

High precision data of dilepton angular distributions in ${\gamma }^{\ast }/Z$ 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 $\cos 2\varphi$ 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. The violation of the Lam-Tung relation is attributed to the presence of a non-zero component of the $q-\bar{q}$ axis in the direction normal to the "hadron plane" formed by the colliding hadrons. The magnitude of the violation of the Lam-Tung relation is shown to reflect the amount of this `non-coplanarity". The observed $q_T$ dependencies of $\lambda$ and $\nu$ from the CMS and the earlier CDF data can be well described using this approach.

5 pages, 3 figures

References in corpus (5)

• Angular coefficients of Z bosons produced in pp collisions at sqrt(s) = 8 TeV and decaying to mu+mu- as a function of transverse momentum and rapidity
• First Measurement of the Angular Coefficients of Drell-Yan $e^{+}{e}^{-}$ pairs in the Z Mass Region from $p\bar{p}$ Collisions at $\sqrt{s}$ = 1.96 TeV
• Extracting Boer-Mulders functions from $p+D$ Drell-Yan processes
• Model-independent constraints on the shape parameters of dilepton angular distributions
• Angular distribution of leptons from the decay of massive vector bosons

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