2 research outputs found
Heavy flavours in AA collisions: production, transport and final spectra
A multi-step setup for heavy-flavour studies in high-energy nucleus-nucleus
(AA) collisions --- addressing within a comprehensive framework the initial
Q-Qbar production, the propagation in the hot medium until decoupling and the
final hadronization and decays --- is presented. The initial hard production of
Q-Qbar pairs is simulated using the POWHEG pQCD event generator, interfaced
with the PYTHIA parton shower. Outcomes of the calculations are compared to
experimental data in pp collisions and are used as a validated benchmark for
the study of medium effects. In the AA case, the propagation of the heavy
quarks in the medium is described in a framework provided by the relativistic
Langevin equation. For the latter, different choices of transport coefficients
are explored (either provided by a perturbative calculation or extracted from
lattice-QCD simulations) and the corresponding numerical results are compared
to experimental data from RHIC and the LHC. In particular, outcomes for the
nuclear modification factor R_AA and for the elliptic flow v_2 of D/B mesons,
heavy-flavour electrons and non-prompt J/\psi's are displayed
Doorway States in the Random-Phase Approximation
By coupling a doorway state to a see of random background states, we develop
the theory of doorway states in the framework of the random-phase approximation
(RPA). Because of the symmetry of the RPA equations, that theory is radically
different from the standard description of doorway states in the shell model.
We derive the Pastur equation in the limit of large matrix dimension and show
that the results agree with those of matrix diagonalization in large spaces.
The complexity of the Pastur equation does not allow for an analytical approach
that would approximately describe the doorway state. Our numerical results
display unexpected features: The coupling of the doorway state with states of
opposite energy leads to strong mutual attraction