# APC

The following figures show the results for energy loss of an energetic gluon propagating in a thermal gluon plasma with temperature T = 300 MeV. The size of the "brick" is 8 x 8 x 20 fm and the gluon distribution is taken as a thermal Boltzmann distribution for massless gluons. All calculations were performed by Ghi R. Shin.

The calculations are performed in two modes: (1) Including both, elastic (gg -> gg) and inelastic (gg -> ggg) processes, and (2) elastic (gg - > gg) scattering only. The QCD coupling constant is held fixed at αs = 0.3; the differential cross sections have infrared cut-offs from a screening mass ${\displaystyle m_{D}={\sqrt {6}}gT/\pi }$. The radiative cross section implements the LPM effect in a probabilistic form. The detailed form of the cross sections and the method of solution is described in: G.R. Shin and B. Müller, J. Phys. G 28 (2002) 2643.

Above: Energy dependence of gluon cross sections used in the Andong Parton Cascade.

The following figures are all for a gluon moving through a gluon bath with T= 300 MeV. They are plotted versus time t, which corresponds to the pathlength x as long as the trajectory is a straight line. The evolution always tracks the most energetic particle (in the bath frame) emerging from the collision.

The figures above show that the energy decreases exponentially as a function of time; for short times the energy decay is linear. The energy loss due to elastic scattering is much less than the inelastic energy loss.

The first figure above, including both elastic and inelastic energy loss, show that the rate of energy loss, dE/dt, for a given energy E is independent of the initial energy of the parton.

The figures above show the time evolution of the transverse momentum broadening ${\displaystyle \langle p_{T}^{2}\rangle }$ of the parton. The first figure shows nicely how the energetic parton thermalizes in a sufficiently thick medium when both, elastic and inelastic processes are included. Elastic energy loss alone is insufficient to lead to thermalization on the distance scales explored here.

(Created by Berndt Müller on September 8th 2008.)