Measurement of the Lund plane for light- and beauty-quark jets

TL;DR

This paper presents the first measurement of the Lund jet plane for light and beauty quark jets at the LHCb, providing insights into QCD radiation patterns and observing the dead-cone effect in beauty jets.

Contribution

First measurement of the Lund jet plane for light and beauty quark jets at 13 TeV, enabling tests of QCD splitting functions and observing the dead-cone effect.

Findings

First direct observation of the dead-cone effect in beauty-quark jets.

Comparison of jet substructure for light and beauty quarks.

Validation of QCD predictions across different radiation regimes.

Abstract

The substructure of jets in quantum chromodynamics (QCD) has garnered significant attention with the advent of infrared- and collinear-safe clustering algorithms and observables. A key question emerging from these studies is how in-jet emissions at soft and hard energy scales, across collinear and wide angles relative to the emitter, differ with the mass of the emitting parton. The Lund jet plane (LJP) is a perturbatively well-defined substructure observable that maps the radiation pattern of jets onto a plane, visually distinguishing emissions with different kinematic properties. Comparing LJP for jets containing hadrons of low versus high mass enables the testing of QCD splitting functions from first-principles calculations across both soft and hard regimes and at different radiation angles. This article presents the first measurement of the LJP for light-quark-enriched and beauty-initiated jets at center-of-mass energy of 13\tev at LHCb. This marks the first direct observation of the dead-cone effect in beauty-quark jets, measured in the collinear region of the LJP.