# Lepton angular distribution of Z boson production and jet discrimination

## TL;DR

This paper analyzes lepton angular distributions in Z boson production, revealing how jet composition affects angular coefficients and the Lam-Tung relation, offering new methods for jet discrimination and predictions for future data tests.

## Contribution

It introduces a geometric approach to understand angular distributions and predicts distinct differences in coefficients for quark versus gluon jets, aiding jet discrimination techniques.

## Key findings

- $A_0$ and $A_2$ differ significantly between quark and gluon jet events.
- The Lam-Tung relation is more violated in multi-jet events than in inclusive data.
- Predictions are testable with existing LHC data.

## Abstract

High precision data of lepton angular distributions in inclusive $Z$ boson production, reported by the CMS and ATLAS Collaborations, showed pronounced transverse momentum ($q_T$) dependencies of the $A_0$ and $A_2$ coefficients. Violation of the Lam-Tung relation, $A_0 = A_2$, was also found. An intuitive understanding of these results can be obtained from a geometric approach. 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. 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.