Speaker
Description
Hard probes, due to their large momenta (or masses), are produced only through hard interactions with large momentum transfer at the earliest phase of a heavy-ion collision. They then propagate through the evolving medium probing QCD matter at different energy scales and different phases of the fireball evolution. During this propagation heavy quarks and high-$p_T$ partons lose a substantial fraction of their initial energy. While machanisms of the energy losses are quite well understood in equilibrated QGP, the influence of pre-equilibrium phases on transport of hard probes has been only fragmentarily explored.
In the talk, I will demonstrate that the glasma can indeed play an important role in transport of hard probes. I will discuss the transverse momentum broadening coefficient $\hat q$ and collisional energy loss $dE/dx$ of hard probes moving through the glasma. First, I will present the methodology that is used to compute the transport coefficients: the Fokker-Planck equation, whose collision terms determine $\hat q$ and $dE/dx$, and the proper time expansion that describes the temporal evolution of the glasma. The correlators of chromodynamic fields that determine the Fokker-Planck collision terms are computed to fifth order. The transport coefficients are shown to be strongly dependent on time and orientation of the probe's velocity. They are large, $\hat q$ is of the order of a few ${\rm GeV^2/fm}$ and $dE/dx \sim 1~{\rm GeV/fm}$, in the domain of validity of the proper time expansion and their values depend on the probe's velocity ${\bf v}$ and the parameters: coupling constant $g$, saturation momentum $Q_s$ (UV scale), and IR regulator $m$, fixed by the confinement scale. I will show how $\hat q$ depends on all these quantities. Different regularization procedures will be also analysed and shown to lead to similar results for $\hat q$. Finally, I will discuss limitations of the whole our approach, such as the validity of the proper-time expansion and constraints resulting from the Fokker-Planck equation.
