The Time Substructure of Jets and Boosted Object Tagging

TL;DR

This paper explores the time substructure of jets, proposing that analyzing hadron arrival times can improve boosted object tagging by distinguishing electroweak boson jets from QCD jets.

Contribution

It introduces the concept of time substructure in jets and demonstrates how charged hadron arrival times can enhance boosted object identification.

Findings

Velocity distribution of jet hadrons relates to color string properties

Boosted color singlet jets have distinct velocity distributions

Timing cuts improve discrimination of electroweak boson jets from QCD jets

Abstract

We initiate the study of the time substructure of jets, motivated by the fact that the next generation of detectors at particle colliders will resolve the time scale over which jet constituents arrive. This effect is directly related to hadronization, which transforms partons into massive hadrons with a distribution of velocities. We review the basic predictions for the velocity distribution of jet hadrons, and suggest an application for this information in the context of boosted object tagging. By noting that the velocity distribution is determined by the properties of the color string which ends on the parton that initiates the jet, we observe that jets originating from boosted color singlets, such as Standard Model electroweak bosons, will exhibit velocity distributions that are boosted relative to QCD jets of similar jet energy. We find that by performing a simple cut on the corresponding distribution of charged hadron arrival times at the detector, we can discriminate against QCD jets that would otherwise give a false positive under a traditional spatial substructure based boosted object tagger.