Abstract
We present a study of the directed flow v1 for D mesons discussing both the impact of initial vorticity and electromagnetic field. Recent studies predicted that v1 for D mesons is expected to be surprisingly much larger than that of light charged hadrons; we clarify that this is due to a different mechanism leading to the formation of a directed flow with respect to the one of the bulk matter at both relativistic and non-relativistic energies. We point out that the very large v1 for D mesons can be generated only if there is a longitudinal asymmetry between the bulk matter and the charm quarks and if the latter have a large non-perturbative interaction in the QGP medium. A quite good agreement with the data of STAR and ALICE is obtained if the diffusion coefficient able to correctly predict the RAA(pT), v2(pT) and v3(pT) of D meson is employed. Furthermore, the mechanism for the build-up of the v1(y) is associated to a quite small formation time that can be expected to be more sensitive to the initial high-temperature dependence of the charm diffusion coefficient.We discuss also the splitting of v1 for D0 and {overline{D}}^0 due to the electromagnetic field that is again much larger than the one observed for charged particles and in agreement with the data by STAR that have however still error bars comparable with the splitting itself, while at LHC standard electromagnetic profile assuming a constant conductivity is not able to account for the huge splitting observed.
Highlights
We discuss the splitting of v1 for D0 and D 0 due to the electromagnetic field that is again much larger than the one observed for charged particles and in agreement with the data by STAR that have still error bars comparable with the splitting itself, while at LHC standard electromagnetic profile assuming a constant conductivity is not able to account for the huge splitting observed
We have presented a study of the build-up of the directed flow of charm quarks at both RHIC and LHC energy
The predictions have been obtained by means of realistic simulation of the uRHICs based on relativistic Boltzmann transport equation evolving on initial conditions that take into account both the vorticity of the created matter and its tilted longitudinal distribution as well as the action of the electromagnetic fields
Summary
We use a relativistic transport code developed to perform studies of the dynamics of heavyion collisions at both RHIC and LHC energies and different collision systems [66,67,68,69,70,71,72,73,74,75]. The initial conditions for the bulk in the coordinate space are given by the standard Glauber model assuming boost invariance along the longitudinal direction In momentum space they are given by a Boltzmann-Jüttner distribution function up to transverse momentum pmT j while at larger momenta we adopt mini-jet distributions as calculated by pQCD at NLO order in [80]: we take pmT j = 2.0 GeV at RHIC and pmT j = 3.5 GeV at LHC energy. In the above equation By+(τ, ηs, x⊥, φ) and By−(τ, ηs, x⊥, φ) are the elementary magnetic fields generated by a single charge e located in the transverse plane at x⊥ = (x⊥, φ) and moving towards +z and −z respectively with speed β related to the longitudinal space-time rapidity ηs; xin and xout are the endpoints of the x⊥ integration regions given by b xin/out(φ ) = ∓ 2 cos(φ ) +. The inclusion of the electromagnetic field does not affect visibly those quantities, while it produces a sizeable effect on the rapidity dependence of the directed flow v1 of D0 and D0 as we will see
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