Collimation of average multiplicity in QCD jets

TL;DR

This paper studies how the distribution of particles within quark and gluon jets becomes more focused or spread out, using advanced QCD calculations, and compares elementary and heavy-ion collision environments.

Contribution

It introduces higher order corrections in QCD jet collimation analysis and explores medium effects in heavy-ion collisions, extending previous leading order studies.

Findings

Higher order corrections reduce jet multiplicity collimation.

Jet broadening is observed in QCD media at all energies.

Medium-modified splitting functions enhance infrared effects.

Abstract

The collimation of average multiplicity inside quark and gluon jets is investigated in perturbative QCD in the modified leading logarithmic approximation (MLLA). The role of higher order corrections accounting for energy conservation and the running of the coupling constant leads to smaller multiplicity collimation as compared to leading logarithmic approximation (LLA) results. The collimation of jets produced in heavy-ion collisions has also been explored by using medium-modified splitting functions enhanced in the infrared sector. As compared to elementary collisions, the angular distribution of the jet multiplicity is found to broaden in QCD media at all energy scales.