Secondary Lund jet plane as a gluon enriched sample

TL;DR

This paper introduces a novel method to select high-purity gluon-initiated jets at the LHC by analyzing the primary Lund plane density in a specific dijet topology, achieving around 90% gluon purity.

Contribution

The paper presents a new strategy using the Lund jet plane to obtain a high-purity gluon jet sample without relying on taggers or statistical separation.

Findings

Achieves approximately 90% gluon purity in the selected jet sample.

The gluon purity is robust against event color structure, hard process flavor, and PDFs.

The method is practical for LHC analyses and constrains gluon radiation patterns.

Abstract

We propose a new strategy to obtain a high-purity sample of gluon-initiated jets at the LHC. Our approach, inspired by the Lund jet plane picture, is to perform a dijet selection where the two jets are collinear to each other and their momentum fraction share is highly asymmetric, and to measure the primary Lund plane density of emissions of the subleading jet. The subleading jet in this topology is practically equivalent to a secondary Lund jet plane. We demonstrate by means of fixed-order calculations that such a simple setup yields gluon jet fractions of around 90% for the subleading jet for both quark- and gluon-initiated jets. This observation is confirmed using hadron-level Monte Carlo generated events. We also show that the extracted gluon purities are highly resilient to the overall colour structure of the event, to the flavour of the hard-scattering process, and to the parton distribution functions. This strategy is well-suited for constraining the radiation pattern of gluon-initiated jets using a set of fiducial cuts that can readily be tested at the LHC, without relying on taggers or statistical demixing.