Investigation of the difference in the angular distributions of $Z\to {\ell }^{+}{\ell }^{-}$ events produced in quark-antiquark, quark-gluon and gluon-gluon collisions

Abstract

Measurements of the angular distributions of Z boson-decay leptons at the Large Hadron Collider (LHC) are of interest in QCD studies and precision electroweak measurements. Z boson production at the LHC is dominated by quark-gluon processes and the quark-antiquark process accounts for only 40\% of the cross section. We investigate the theoretical predictions (using the POWHEG-minnlops event generator) for the difference in the angular distributions of $pp\to {\gamma }^{\ast }/Z\to {\ell }^{+}{\ell }^{-}$ (${\mu }^{+}{\mu }^{-}$ or $e^{+}{e}^{-}$) events produced via quark-antiquark, quark-gluon , and gluon-gluon processes. The study is done for proton-proton collisions at the Large Hadron Collider (LHC) at $\sqrt{s}=13$ TeV. We investigate the angular coefficients $A_0$ and $A_2$ (for ${\theta }_{CS}$ and ${\varphi }_{CS}$ distributions in the Collins-Soper frame) for the different processes as a function of the Z boson rapidity, transverse momentum and final state jet multiplicity, and propose how these can be investigated experimentally at the LHC.

10 pages, 8 figures, submitted to Phys. Rev. D