3,290 research outputs found
Heavy flavours in heavy-ion collisions: quenching, flow and correlations
We present results for the quenching, elliptic flow and azimuthal
correlations of heavy flavour particles in high-energy nucleus-nucleus
collisions obtained through the POWLANG transport setup, developed in the past
to study the propagation of heavy quarks in the Quark-Gluon Plasma and here
extended to include a modeling of their hadronization in the presence of a
medium. Hadronization is described as occurring via the fragmentation of
strings with endpoints given by the heavy (anti-)quark Q(Qbar) and a thermal
parton qbar(q) from the medium. The flow of the light quarks is shown to affect
significantly the R_AA and v_2 of the final D mesons, leading to a better
agreement with the experimental data. The approach allows also predictions for
the angular correlation between heavy-flavour hadrons (or their decay
electrons) and the charged particles produced in the fragmentation of the
heavy-quark strings
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.Comment: 16 pages, 21 figure
ONE-TROCAR VIDEO-ASSISTED STRIPPING TECHNIQUE FOR USE IN THE TREATMENT OF LARGE OVARIAN CYSTS IN INFANTS
Background
Management of ovarian cysts in infants is controversial; it can be conservative or surgical, and the management is determined by the cyst''s size and sonographic features.
Methods
A surgical approach using a 10-mm umbilically placed operative laparoscope was taken in 3 female infants with antenatally diagnosed large, simple ovarian cysts. The contents of the cysts were partially aspirated and the cyst walls were stripped off the remaining ovarian parenchyma. No intraoperative or postoperative complications were recorded.
Conclusions
The one-trocar video-assisted stripping technique for large ovarian cysts in infants appears to be an ovarian-tissue-preserving procedure, and it sidesteps the disadvantages of large scars and formation of adhesions
Space-like and time-like pion electromagnetic form factor and Fock state components within the Light-Front dynamics
The simultaneous investigation of the pion electromagnetic form factor in the
space- and time-like regions within a light-front model allows one to address
the issue of non-valence components of the pion and photon wave functions. Our
relativistic approach is based on a microscopic vector meson dominance (VMD)
model for the dressed vertex where a photon decays in a quark-antiquark pair,
and on a simple parametrization for the emission or absorption of a pion by a
quark. The results show an excellent agreement in the space like region up to
-10 , while in time-like region the model produces reasonable
results up to 10 .Comment: 74 pages, 11 figures, use revtex
Langevin dynamics of heavy flavors in relativistic heavy-ion collisions
We study the stochastic dynamics of c and b quarks, produced in hard initial
processes, in the hot medium created after the collision of two relativistic
heavy ions. This is done through the numerical solution of the relativistic
Langevin equation. The latter requires the knowledge of the friction and
diffusion coefficients, whose microscopic evaluation is performed treating
separately the contribution of soft and hard collisions. The evolution of the
background medium is described by ideal/viscous hydrodynamics. Below the
critical temperature the heavy quarks are converted into hadrons, whose
semileptonic decays provide single-electron spectra to be compared with the
current experimental data measured at RHIC. We focus on the nuclear
modification factor R_AA and on the elliptic-flow coefficient v_2, getting, for
sufficiently large p_T, a reasonable agreement.Comment: Talk given at the workshop "Jets in Proton-Proton and Heavy-Ion
Collisions", Prague, 12th-14th August 201
Event-shape engineering and heavy-flavour observables in relativistic heavy-ion collisions
Traditionally, events collected at relativistic heavy-ion colliders are
classified according to some centrality estimator (e.g. the number of produced
charged particles) related to the initial energy density and volume of the
system. In a naive picture the latter are directly related to the impact
parameter of the two nuclei, which sets also the initial eccentricity of the
system: zero in the case of the most central events and getting larger for more
peripheral collisions. A more realistic modelling requires to take into account
event-by-event fluctuations, in particular in the nucleon positions within the
colliding nuclei: collisions belonging to the same centrality class can give
rise to systems with different initial eccentricity and hence different flow
harmonics for the final hadron distributions. This issue can be addressed by an
event-shape-engineering analysis, consisting in selecting events with the same
centrality but different magnitude of the average bulk anisotropic flow and
therefore of the initial-state eccentricity. In this paper we present the
implementation of this analysis in the POWLANG transport model, providing
predictions for the transverse-momentum and angular distributions of charm and
beauty hadrons for event-shape selected collisions. In this way it is possible
to get information on how the heavy quarks propagating (and hadronizing) in a
hot environment respond both to its energy density and to its geometric
asymmetry, breaking the perfect correlation between eccentricity and impact
parameter which characterizes a modelling of the medium based on smooth average
initial condition
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