[en] I review the linearized hydrodynamical treatment of a fast parton traversing a perturbative quark-gluon plasma. Using numerical solutions for the medium's response to the fast parton, I obtain the medium's distribution function, which is then used in a Cooper-Frye freeze-out prescription to obtain an azimuthal particle spectrum. Two different freeze-out scenarios are considered which yield significantly different results. I conclude that any meaningful comparison of azimuthal hadron correlation functions to RHIC data requires implementing a realistic freeze-out scenario in an expanding medium. (orig.)

[en] I derive the space-time distribution of energy and momentum deposited by a fast parton traversing a perturbative quark-gluon plasma by considering the fast parton as the source of an external color field interacting with the medium. I include the medium's response to screen the fast parton's color field by incorporating dielectric functions and compare to the unscreened result.

[en] I use the space-time distribution of energy and momentum deposited by a fast parton traversing a perturbative quark-gluon plasma as a source term for the linearized hydrodynamical equations of the medium. A method of solution for the medium response is presented in detail. Numerical results are given for different values of the shear viscosity to entropy density ratio, η/s, and speed of sound, c_s. Furthermore, I investigate the relevance of finite source structure by expanding the source term up to first order in gradients of a δ function centered at the fast parton and comparing the resulting dynamics to that obtained with the full source. It is found that, for the source term used here, the medium response is sensitive to the finite source structure up to distances of several femtometers from the source parton.

[en] We calculate the total energy deposited into the medium per unit length by fast partons traversing a quark-gluon plasma. The medium excitation due to collisions is taken to be given by the well-known expression for the collisional drag force. The radiative energy loss of the parton contributes to the energy deposition because each radiated gluon acts as an additional source of collisional energy loss in the medium. We derive a differential equation which governs how the spectrum of radiated gluons is modified when this energy loss is taken into account. This modified spectrum is then used to calculate the additional energy deposition due to the interactions of radiated gluons with the medium. Numerical results are presented for the medium response for the case of two energetic back-to-back partons created in a hard interaction.

[en] The heavy ion program at the LHC will present unprecedented opportunities to probe hot QCD matter, that is, the quark gluon plasma (QGP). Among these exciting new probes are high energy partons associated with the production of a Z⁰ boson, or Z⁰ tagged jets. Once produced, Z⁰ bosons are essentially unaffected by the strongly interacting medium produced in heavy-ion collisions, and therefore provide a powerful signal of the initial partonic energy and subsequent medium induced partonic energy loss. When compared with theory, experimental measurements of Z⁰ tagged jets will help quantify the jet quenching properties of the QGP and discriminate between different partonic energy loss formalisms. In what follows, I discuss the advantages of tagged jets over leading particles, and present preliminary results of the production and suppression of Z⁰ tagged jets in relativistic heavy-ion collisions at LHC energies using the Guylassy-Levai-Vitev (GLV) partonic energy loss formalism.

[en] A 13-point Thomson scattering system mounted on the JFT-2M tokamak routinely provides reproducible electron temperature and density data. Good performance has been achieved with the help of a large collecting lens (capable of gathering data over a vertical 60-cm long plasma volume), the automatic transfer of data from a 180-channel attenuator into the CPU, the use of high-pass optical filters and a large polarizer plate to reduce stray light, and a better matching of LED calibration signal intensities to those of the scattered signals. Peaked density profiles are measured in improved L-mode (IL) plasmas, in contrast to those observed during the H-mode phase. IL-mode is caused by the broad and high electron temperature. With pellet injection, peaked density profiles are again observed. (author)

[en] I derive the distribution of energy and momentum transmitted from a fast parton to a medium of thermalized quarks, or the source term, in perturbative thermal field theory directly from the quark energy-momentum tensor. The fast parton is coupled to the medium by adding an interaction term to the Lagrangian. The thermal expectation value of the energy-momentum tensor source term is then evaluated using standard Feynman rules at finite temperature. It is found that local excitations, which are important for exciting an observable Mach cone structure, fall sharply as a function of the energy of the fast parton. This may have implications for the trigger p_T dependence of measurements of azimuthal dihadron particle correlations in heavy-ion collisions. In particular, a conical emission pattern would be less likely to be observed for increasing trigger p_T. I show that the results presented in this paper can be generalized to more realistic modeling of fast parton propagation, such as through a time-dependent interaction term, in future studies.

[en] A receiving system for a Thomson scattering experiment is described. This system includes a multichannel grating spectrometer designed for use with a high repetition rate Nd:YAG laser. Fiber-optic coupling bundles are used at the input and output ends. High throughput is maintained with large-diameter, low f-number grating and aspheric lenses. The detectors are high-responsivity, temperature-compensated avalanche photodiodes. Results of the calibration, including anti-Stokes Raman scattering, are presented. The spectrometer is designed to operate in the T/sub e/ range between 50 eV and 2 keV with a minimum electron density sensitivity of 1.6 x 10¹¹ cm^-3

[en] The distribution of energy and momentum deposited by a fast parton in a medium of thermalized quarks, or the source term, is evaluated in perturbative thermal field theory. The calculation is performed by directly evaluating the thermal expectation value of the quark energy-momentum tensor. The fast parton is coupled to the medium by adding an interaction term to the Lagrangian. I show that this approach is very general and can be modified to consider more realistic modeling of fast parton propagation, such as a fast parton created in an initial hard interaction or the evolution of a parton shower due to medium induced radiation. For the scenario considered here, it is found that local excitations fall sharply as a function of the energy of the fast parton. These local excitations couple directly to the sound mode in hydrodynamics and are important for generating an observable shockwave structure. This may have implications for the trigger p_T dependence of measurements of azimuthal dihadron particle correlations in heavy-ion collisions. In particular, one would be less likely to observe a conical emission pattern for increasing trigger p_T.

[en] Particle correlation measurements associated with a hard or semihard trigger in heavy-ion collisions may reflect Mach cone shock waves excited in the bulk medium by partonic energy loss. This is of great interest because, when compared with theory, such measurements can provide information on the transport properties of the medium. Specifically, the formation of Mach cone shock waves is sensitive to the viscosity and speed of sound, as well as the detailed nature of the jet-medium interaction. However, modeling the physics of shock-wave excitation to obtain a meaningful comparison with measured correlations is very challenging, as the correlations arise from an interplay of perturbative as well as nonperturbative phenomena at different momentum scales. In this work we take a step in that direction by presenting a systematic study of the dependence of azimuthal particle correlations on the spatiotemporal structure of energy deposition into the medium. Our results indicate that detailed modeling of the evolution of an initially produced hard parton and the interaction of this evolving state with the medium is crucial, as both the magnitude and the shape of the shock-wave signal show a strong dependence on the assumptions being made.