Heavy quark energy loss far from equilibrium in a strongly coupled collision
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Rajagopal_Heavy quark.pdf
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Author(s)
Chesler, Paul Michael
Lekaveckas, Mindaugas
Rajagopal, Krishna
Date Issued
October 2013
Journal
Journal of High Energy Physics
Publisher
Springer-Verlag
Citation
Chesler, Paul M., Mindaugas Lekaveckas, and Krishna Rajagopal. “Heavy Quark Energy Loss Far from Equilibrium in a Strongly Coupled Collision.” J. High Energ. Phys. 2013, no. 10 (October 2013).
Version
Final published version
Abstract
We compute and study the drag force acting on a heavy quark propagating through the matter produced in the collision of two sheets of energy in a strongly coupled gauge theory that can be analyzed holographically. Although this matter is initially far from equilibrium, we find that the equilibrium expression for heavy quark energy loss in a homogeneous strongly coupled plasma with the same instantaneous energy density or pressure as that at the location of the quark describes many qualitative features of our results. One interesting exception is that there is a time delay after the initial collision before the heavy quark energy loss becomes significant. At later times, once a liquid plasma described by viscous hydrodynamics has formed, expressions based upon assuming instantaneous homogeneity and equilibrium provide a semi-quantitative description of our results — as long as the rapidity of the heavy quark is not too large. For a heavy quark with large rapidity, the gradients in the velocity of the hydrodynamic fluid result in qualitative consequences for the ‘drag’ force acting on the quark. In certain circumstances, the force required to drag the quark through the plasma can point opposite to the velocity of the quark, meaning that the force that the plasma exerts on a quark moving through it acts in the same direction as its velocity. And, generically, the force includes a component perpendicular to the direction of motion of the quark. Our results support a straightforward approach to modeling the drag on, and energy loss of, heavy quarks with modest rapidity in heavy ion collisions, both before and after the quark-gluon plasma hydrodynamizes, and provide cautionary lessons at higher rapidity.
MIT Department
Massachusetts Institute of Technology. Center for Theoretical Physics
Massachusetts Institute of Technology. Department of Physics
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DOI of Published Version
https://doi.org/10.1007/jhep10(2013)013
