QCD Evolution of Jets in the Quark-Gluon Plasma

TL;DR

This paper introduces a new QCD evolution formalism for jets in the quark-gluon plasma, combining parton radiation and scattering, to better understand jet quenching in heavy ion collisions.

Contribution

It develops two approaches to include medium interactions in jet evolution, extending DGLAP equations and incorporating transverse momentum dependence.

Findings

Significant jet softening depending on plasma temperature.

Enhanced effects at LHC energies compared to RHIC.

Framework facilitates comparison with experimental data.

Abstract

The quark-gluon plasma (QGP) can be explored in relativistic heavy ion collisions by the jet quenching signature, i.e. by the energy loss of a high energy quark or gluon traversing the plasma. We introduce a novel QCD evolution formalism in the leading logarithm approximation, where normal parton radiation is interleaved with scattering on the plasma gluons occuring at a similar time scale. The idea is elaborated in two approaches. One extends the DGLAP evolution equations for fragmentation functions to include scatterings in the medium, which facilitates numerical solutions for comparison with data and provides a basis for a Monte Carlo implementation. The other approach is more general by including also the transverse momentum dependence of the jet evolution, which allows a separation of the scales also for the scattering term and provides a basis for analytical investigations. The two approaches are shown to be related and give the same characteristic softening of the jet depending on the temperature of the plasma. A substantial effect is found at the RHIC energy and is further enhanced at LHC. Systematic studies of data on the energy loss could, therefore, demonstrate the existence of the QGP and probe its properties.