Jet energy loss in quark-gluon plasma

Deke Sun, Purdue University

Abstract

This dissertation discusses my investigations of energy loss of high-momentum quarks and gluons in the quark-gluon plasma (QGP). Two different jet energy loss mechanisms, elastic (collisional) energy loss and radiative energy loss, are studied extensively. Frame-independent treatments of Gyulassy-Levai-Vitev (GLV) radiative energy loss for light partons, Djordjevic-Gyulassy-Levai-Vitev (DGLV) radiative energy loss for heavy quarks, and Thoma-Gyulassy (TG) elastic energy loss, as well as of a simple dE/dL radiative energy loss, are formulated and applied to energy loss calculations for both light parton and heavy quark jets in heavy ion collisions at both Relativistic Heavy-ion Collider (RHIC) and the Large Hadron Collider (LHC) energies, using different medium evolution models. In Chapter 2 two of the major findings regarding radiative energy loss are discussed: • realistic medium transverse expansion suppresses elliptic flow v2 significantly because (D)GLV energy loss biases for later time interaction, when the medium is more azimuthally symmetric; • covariant frame-independent treatment of (D)GLV energy loss increases v2 by about 50%, significantly improving simultaneous agreement with experimental data on the nuclear modification factor RAA and elliptic flow v2. This is because covariance leads to an interplay between the jet propagation direction and the collective flow of medium, causing an enhanced in-plane versus out-of-plane energy loss difference. In Chapter 3 elastic energy loss is studied in detail, and two main conclusions are drawn: • compared to original TG elastic energy loss, covariant TG energy loss increases v2, especially at relatively low transverse momentum (pT); and • compared to purely radiative (D)GLV energy loss, purely elastic TG energy loss exhibits a half as large v2. After detailed discussion of radiative and elastic energy loss, Chapter 4 presents results with both radiative and elastic energy loss included, and shows that the combined elastic+radiative energy loss results in a significantly smaller v2 than purely radiative energy loss. This is true even after parameters are adjusted to reproduce the same RAA(pT) for neutral pions (π0). Chapter 5 investigates the event-by-event correlation between jet flow and medium geometry. High correlations between the jet elliptic flow v2 and the initial medium eccentricity ϵ2, as well as between the jet and the medium elliptic flow, are demonstrated.

Degree

Ph.D.

Advisors

Molnar, Purdue University.

Subject Area

Physics|Nuclear physics|Particle physics

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