# Comparison of fragmentation functions for light-quark- and gluon-dominated jets from $pp$ and Pb+Pb collisions in ATLAS

## TL;DR

This paper measures charged-particle fragmentation functions in proton-proton and lead-lead collisions at 5.02 TeV, comparing them to Monte Carlo predictions and exploring jet quenching effects related to parton type and collision centrality.

## Contribution

It provides the first detailed comparison of photon-tagged and inclusive jet fragmentation functions in heavy-ion collisions, revealing differences in jet quenching based on parton flavor and collision centrality.

## Key findings

- Fragmentation functions differ between photon-tagged and inclusive jets in pp collisions.
- Photon-tagged jets show larger modifications in central Pb+Pb collisions.
- Results support parton color-charge dependence of jet quenching.

## Abstract

Charged-particle fragmentation functions for jets azimuthally balanced by a high-transverse-momentum, prompt, isolated photon are measured in $25$ pb$^{-1}$ of $pp$ and $0.49$ nb$^{-1}$ of Pb+Pb collision data at $5.02$ TeV per nucleon pair recorded with the ATLAS detector at the Large Hadron Collider. The measurements are compared to predictions of Monte Carlo generators and to measurements of inclusively selected jets. In $pp$ collisions, a different jet fragmentation function in photon-tagged events from that in inclusive jet events arises from the difference in fragmentation between light quarks and gluons. The ratios of the fragmentation functions in Pb+Pb events to that in $pp$ events are used to explore the parton color-charge dependence of jet quenching in the hot medium. In relatively peripheral collisions, fragmentation functions exhibit a similar modification pattern for photon-tagged and inclusive jets. However, photon-tagged jets are observed to have larger modifications than inclusive jets in central Pb+Pb events.