Measurement of jet track functions in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

TL;DR

This paper reports a direct measurement of the transverse momentum fraction carried by charged hadrons in jets from 13 TeV proton-proton collisions, providing data to test and refine QCD predictions for jet substructure.

Contribution

It presents the first direct measurement of track functions in dijet events at the LHC, using machine learning for detector correction and comparing results with QCD predictions.

Findings

Measured the $r_q$ distribution in dijet events

Compared scale evolution of moments with QCD predictions

Data will improve theoretical calculations of jet substructure

Abstract

Measurements of jet substructure are key to probing the energy frontier at colliders, and many of them use track-based observables which take advantage of the angular precision of tracking detectors. Theoretical calculations of track-based observables require `track functions', which characterize the transverse momentum fraction $r_q$ carried by charged hadrons from a fragmenting quark or gluon. This letter presents a direct measurement of $r_q$ distributions in dijet events from the 140 fb$^{-1}$ of proton--proton collisions at $\sqrt{s}=13$ TeV recorded with the ATLAS detector. The data are corrected for detector effects using machine-learning methods. The scale evolution of the moments of the $r_q$ distribution is sensitive to non-linear renormalization group evolution equations of QCD, and is compared with analytic predictions. When incorporated into future theoretical calculations, these results will enable a precision program of theory-data comparison for track-based jet substructure observables.