Open heavy flavor in QCD matter and in nuclear collisions

Abstract

We review the experimental and theoretical status of open heavy-flavor (HF) production in high-energy nuclear collisions at RHIC and LHC. We first overview the theoretical concepts and pertinent calculations of HF transport in QCD matter, including perturbative and non-perturbative approaches in the quark-gluon plasma, effective models in hadronic matter, as well as implementations of heavy-quark (HQ) hadronization. This is followed by a brief discussion of bulk evolution models for heavy-ion collisions and initial conditions for the HQ distributions which are needed to calculate HF spectra in comparison to observables. We then turn to a discussion of experimental data that have been collected to date at RHIC and LHC, specifically for the nuclear suppression factor and elliptic flow of semileptonic HF decays, D mesons, non-prompt J/ψ from B-meson decays, and b-jets. Model comparisons to HF data are conducted with regards to extracting the magnitude, temperature and momentumdependence of HF transport coefficients from experiment.

Heavy quarks in turbulent QCD plasmas

“…It has been long believed that the interaction of heavy quarks is significantly weaker than that of light quarks or gluons but experimental data clearly contradict the expectation. As discussed in the review [3], the behavior of mesons containing a heavy quark is rather similar to that of light mesons at both small and large transverse momenta. The problem is not fully resolved.…”

“…the review [3]. Thanks to their large masses the quarks are produced only at the earliest stage of the collision due to hard interactions of partons from incoming nuclei.…”

Non-perturbative Approach to Equation of State and Collective Modes of the QGP

“…On the contrary, for the WCS both transport coefficients are significantly larger and rather constant with temperature. Especially the HQ diffusion coefficient acquires magnitudes which do not compare well with current extractions from HF phenomenology in high-energy heavy-ion collisions [4].…”

“…For the HQ friction coefficient, we extend previous T -matrix calculations carried out for the free and internal energies as potential proxies [4,13,25]. In particular, due to the large widths in the SCS we account for off-shell effects based on the formalism described in Ref.…”

“…The microscopic structure of the sQGP, including its prevalent degrees of freedom and its possible relation to the nearby phase transition(s) into hadronic matter, remains a forefront topic in contemporary research. In addition to the low viscosity inferred from fluid-dynamic models for the bulk evolution of the medium in heavy-ion collisions at RHIC and the LHC, the large modifications observed for the spectra and elliptic flow of heavy-flavor hadrons [4] have provided a more direct evidence of a frequent rescattering that (heavy) quarks undergo throughout the expansion NA60 Data hadronic QGP total thermal Figure 1. Dimuon excess spectra (after subtraction of background and the final-state hadron decay cocktail) [7] compared to theoretical calculations of thermal radiation from an expanding fireball with contributions from the QGP and hadronic phase with in-medium ρ and ω spectral functions; figure taken from Ref.…”