Lepton angular distribution of Z boson production and jet discrimination

Abstract

High precision data of lepton angular distributions in inclusive Z boson production, reported by the CMS and ATLAS Collaborations, showed pronounced transverse momentum (qT) dependencies of the A0 and A2 coefficients. Violation of the Lam-Tung relation, A0=A2, was also found. An intuitive understanding of these results can be obtained from a geometric approach. We predict that A0 and A2 for Z plus single gluon-jet events are very different from that of Z plus single quark-jet events, allowing a new experimental tool for checking various algorithms which attempt to discriminate quark jets from gluon jets. We also predict that the Lam-Tung relation would be more severely violated for the Z plus multiple-jet data than what has been observed so far for inclusive Z production data. These predictions can be readily tested using existing LHC data. Keywords: Z-boson production, Z decay angular distribution, Jet discrimination