Charmonium in a weakly coupled quark-gluon plasma

We present a model of charmonium as two heavy quarks propagating classically in a weakly coupled quark-gluon plasma. The quarks interact via a static, color-dependent potential and also suffer collisions with the plasma particles. We calculate the radiation width of the color octet state (for fixed, classical $q\bar q$ separation) and find that it is long-lived provided a finite gluon mass is used to provide a threshold energy.Comment: 7 pages in plain LaTeX + 3 figures packed with uufiles; slight changes to comply with referees, added one referenc

Passage of charmed particles through the mixed phase in high-energy heavy-ion collisions

We employ a modified cascade hydrodynamics code to simulate the phase transition of an expanding quark-gluon plasma and the passage of a charmed particle through it. When inside the plasma droplets, the charmed quark experiences drag and diffusion forces. When outside the plasma, the quark travels as a $D$ meson and experiences collisions with pions. Additional energy transfer takes place when the quark enters or leaves a droplet. We find that the transverse momentum of $D$ mesons provides a rough thermometer of the phase transition.Comment: 20 pages, 9 Postscript figures included with epsfig.st

Heavy quarkonia in a medium as a quantum dissipative system: Master-equation approach

The problem of the evolution of a heavy quarkonium in a medium can be recast as that of a quantum dissipative system. Within the framework of the master-equation approach to open quantum systems, we consider the real-time dynamics of quarkonia. We find that in a plasma at fixed temperature, the populations of the various quarkonium states evolve together, while their momentum distribution satisfies a Fokker-Planck equation.Comment: 12 pages, 8 figures. Version 2 matches the published versio

Feasibility of dose painting using volumetric modulated arc optimization and delivery

PURPOSE: Dose painting strategies are limited by optimization algorithms in treatment planning systems and physical constraints of the beam delivery. We investigate dose conformity using the RapidArc optimizer and beam delivery technique. Furthermore, robustness of the plans with respect to positioning uncertainties are evaluated. METHODS: A head&neck cancer patient underwent a [(61)Cu]Cu-ATSM PET/CT-scan. PET-SUVs were converted to prescribed dose with a base dose of 60Gy, and target mean dose 90Gy. The voxel-based prescription was converted into 3, 5, 7, 9, and 11 discrete prescription levels. Optimization was performed in Eclipse, varying the following parameters: MLC leaf width (5mm and 2.5mm), number of arcs (1 and 2) and collimator rotation (0, 15, 30 and 45 degrees). Dose conformity was evaluated using quality volume histograms (QVHs), and relative volumes receiving within ±5% of prescribed dose (Q(0.95–1.05)). Deliverability was tested using a Delta4 phantom. Robustness was tested by shifting the isocenter 1mm and 2mm in all directions, and recalculating the dose. RESULTS: Good conformity was obtained using MLC leaf width 2.5mm, two arcs, and collimators 45/315 degrees, with Q(0.95–1.05)=92.8%, 91.6%, 89.7% and 84.6%. Using only one arc or increasing the MLC leaf width had a small deteriorating effect of 2–5%. Small changes in collimator angle gave small changes, but large changes in collimator angle gave a larger decrease in plan conformity; for angles of 15 and 0 degrees (two arcs, 2.5 mm leaf width), Q(0.95–1.05) decreased by up to 15%. Consistency between planned and delivered dose was good, with ~90% of gamma values <1. For 1mm shift, Q(0.95–1.05) was decreased by 5–15%, while for 2mm shift, Q(0.95–1.05) was decreased to 55–60%. CONCLUSIONS: Results demonstrate feasibility of planning of prescription doses with multiple levels for dose painting using RapidArc, and plans were deliverable. Robustness to positional error was low