Momentum broadening in unstable quark-gluon plasma

摘要

Quark-gluon plasma produced at the early stage of ultrarelativistic heavy ioncollisions is unstable, if weakly coupled, due to the anisotropy of itsmomentum distribution. Chromomagnetic fields are spontaneously generated andcan reach magnitudes much exceeding typical values of the fields inequilibrated plasma. We consider a high energy test parton traversing anunstable plasma that is populated with strong fields. We study the momentumbroadening parameter $\hat q$ which determines the radiative energy loss of thetest parton. We develop a formalism which gives $\hat q$ as the solution of aninitial value problem, and we focus on extremely oblate plasmas which arephysically relevant for relativistic heavy ion collisions. The parameter $\hatq$ is found to be strongly dependent on time. For short times it is of theorder of the equilibrium value, but at later times $\hat q$ grows exponentiallydue to the interaction of the test parton with unstable modes and becomes muchbigger than the value in equilibrium. The momentum broadening is also stronglydirectionally dependent and is largest when the test parton velocity istransverse to the beam axis. Consequences of our findings for the phenomenologyof jet quenching in relativistic heavy ion collisions are briefly discussed.