Computing $N$-subjettiness for boosted jets

TL;DR

This paper introduces a new perturbative QCD method to compute jet shapes for boosted jets, specifically the $N$-subjettiness $ au_{21}$ ratio, extending analytic calculations to phenomenologically relevant regions.

Contribution

It presents a novel approach to calculate jet shapes without the small-shape limitation, enabling more accurate predictions for boosted jet substructure analyses.

Findings

Analytic predictions match Monte Carlo simulations.

Extended calculations to the phenomenologically relevant region.

Constructed a decorrelated jet tagger analytically.

Abstract

Jet substructure tools have proven useful in a number of high-energy particle-physics studies. A particular case is the discrimination, or tagging, between a boosted jet originated from an electroweak boson (signal), and a standard QCD parton (background). A common way to achieve this is to cut on a measure of the radiation inside the jet, i.e. a jet shape. Over the last few years, analytic calculations of jet substructure have allowed for a deeper understanding of these tools and for the development of more efficient ones. However, analytic calculations are often limited to the region where the jet shape is small. In this paper we introduce a new approach in perturbative QCD to compute jet shapes for a generic boosted jets, waiving the above limitation. We focus on an example common in the substructure literature: the jet mass distribution after a cut on the $N$-subjettiness $\tau_{21}$ ratio, extending previous works to the region relevant for phenomenology. We compare our analytic predictions to Monte Carlo simulations for both plain and SoftDrop-groomed jets. We use our results to construct analytically a decorrelated tagger.