QCD effects in lepton angular distributions of Drell-Yan/$Z$ production and jet discrimination

TL;DR

This paper compares experimental lepton angular distributions in Drell-Yan and Z production with pQCD calculations, predicts differences in angular coefficients for quark and gluon jets, and explains Lam-Tung relation violation through non-coplanarity effects.

Contribution

It introduces a new method to distinguish quark and gluon jets using angular distribution differences and provides a geometric interpretation of Lam-Tung relation violation.

Findings

Angular distributions match pQCD baseline calculations.

Distinct $A_0$ and $A_2$ for quark vs. gluon jets in Z production.

Violation of Lam-Tung relation linked to non-coplanarity at high transverse momentum.

Abstract

We present a comparison of data of lepton angular distributions of Drell-Yan/$Z$ production with the fixed-order pQCD calculations by which the baseline of pQCD effects is illustrated. As for the $Z$ production, we predict that $A_0$ and $A_2$ 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. Using an intuitive geometric approach, we show that the violation of the Lam-Tung relation, appearing at large transverse-momentum region, is attributed to the presence of a non-coplanarity effect. This interpretation is consistent with the appearance of violation beyond LO-QCD effect.