Pengfei Zhuang

Heavy flavor production serves as an ideal probe of the hadronization mechanism of the quark-gluon plasma created in relativistic heavy ion collisions. We study charm-quark hadronization using Langevin transport in the medium together with a sequential coalescence model. Since D_{s} forms earlier than D^{0}, as obtained from the Dirac equation with an in-medium potential extracted from lattice QCD, the D_{s} elliptic flow v_{2} is smaller than the D^{0} v_{2} in the intermediate-p_{T} region, in good agreement with the recent ALICE data. Incorporating sequential coalescence, charm-quark number conservation, and strangeness enhancement predicts a peak in the yield ratio D_{s}/D^{0} at low p_{T}, which can be tested in future heavy-ion collisions.

We present a relativistic analysis of fermions in an external electric field by non-perturbatively solving the Dirac equation with a static gauge. Different from the magnetic field effect, the fermion wave function in an electric field oscillates asymptotically, which results in the absence of bound states in an infinite system. For a confined fermion, the confinement is gradually canceled by the electric field, and the fermion becomes deconfined when the electric coupling is stronger than the confinement coupling. However, a fermion in an electric field can be confined to a finite system by applying the MIT bag boundary condition, namely, the disappearing normal component of the probability current at the boundary. The solutions obtained can serve as a basis for calculating dynamical processes in the presence of a strong electric field, such as those occurring in the early stage of relativistic heavy-ion collisions, where an extremely strong electric field is expected to be generated.

The magnetic field created in high energy nuclear collisions will affect the dynamical processes in the QCD medium, especially the heavy quark production that happens in the initial stage of the collisions. We calculate in a strong magnetic field the heavy quark production cross section for the elementary process gg {\rightarrow} Q{\bar Q} at leading order and the corresponding transverse momentum distribution in nucleus-nucleus collisions. In comparison to the QED process, the heavy quark production is dominated by the unique QCD channel with gluon self-interaction. Due to the dimension reduction of quark phase space in a strong magnetic field, the production is concentrated in a very narrow energy region above the threshold. Since the translation invariance is broken, the production becomes anisotropic in magnetic field.