Precision Jet Substructure from Boosted Event Shapes

TL;DR

This paper develops a systematic method for calculating jet substructure in high-energy physics using boosted event shapes, enabling precise QCD predictions at the LHC that account for various effects and can be subtracted analytically.

Contribution

It introduces a novel approach to compute jet substructure distributions at high orders by boosting global event shapes, simplifying calculations and handling contamination effects analytically.

Findings

Q-independent 2-subjettiness distribution for Q > 400 GeV

Analytic subtraction of ISR/UE effects at large Q

Q=infinity and Q=0 distributions related by a scaling factor e

Abstract

Jet substructure has emerged as a critical tool for LHC searches, but studies so far have relied heavily on shower Monte Carlo simulations, which formally approximate QCD at leading-log level. We demonstrate that systematic higher-order QCD computations of jet substructure can be carried out by boosting global event shapes by a large momentum Q, and accounting for effects due to finite jet size, initial-state radiation (ISR), and the underlying event (UE) as 1/Q corrections. In particular, we compute the 2-subjettiness substructure distribution for boosted Z -> q qbar events at the LHC at next-to-next-to-next-to-leading-log order. The calculation is greatly simplified by recycling the known results for the thrust distribution in e+ e- collisions. The 2-subjettiness distribution quickly saturates, becoming Q independent for Q > 400 GeV. Crucially, the effects of jet contamination from ISR/UE can be subtracted out analytically at large Q, without knowing their detailed form. Amusingly, the Q=infinity and Q=0 distributions are related by a scaling by e, up to next-to-leading-log order.