2,759 research outputs found
Mini-jet thermalization and diffusion of transverse momentum correlation in high-energy heavy-ion collisions
Transverse momentum correlation in azimuthal angle of produced hadrons due to
mini-jets are studied first within the HIJING Monte Carlo model in high-energy
heavy-ion collisions. Jet quenching in the early stage of thermalization is
shown to lead to significant diffusion (broadening) of the correlation.
Evolution of the transverse momentum density fluctuation that gives rise to
such correlation in azimuthal angle in the later stage of heavy-ion collisions
is further investigated within a linearized diffusion-like equation and is
shown to be determined by the shear viscosity of the evolving dense matter.
Such a diffusion equation for the transverse momentum fluctuation is solved
with initial values given by HIJING and together with the hydrodynamic equation
for the bulk medium. The final transverse momentum correlation in azimuthal
angle is calculated along the freeze-out hyper-surface and is found further
diffused for larger values of shear viscosity to entropy density ratio . Therefore the final transverse momentum correlation in azimuthal
angle can be used to study the thermalization of mini-jets in the early stage
of heavy-ion collisions and the viscous effect in the hydrodynamic evolution of
the strongly coupled quark gluon plasma.Comment: RevTex 4, 4 pages and 2 figures, the method to determine the
fluctuation in transverse fluid velocity in the initial time of the hydro
evolution has been improved. The relevant parts have been rewritten with some
discussions and references adde
Vortical fluid and spin correlations in high-energy heavy-ion collisions
Fermions become polarized in a vortical fluid due to spin-vorticity coupling.
The spin polarization density is proportional to the local fluid vorticity at
the next-to-leading order of a gradient expansion in a quantum kinetic theory.
Spin correlations of two -hyperons can therefore reveal the vortical
structure of the dense matter in high-energy heavy-ion collisions. We employ a
(3+1)D viscous hydrodynamic model with event-by-event fluctuating initial
conditions from A MultiPhase Transport (AMPT) model to calculate the vorticity
distributions and spin correlations. The azimuthal correlation of the
transverse spin is shown to have a cosine form plus an offset due to a circular
structure of the transverse vorticity around the beam direction and global spin
polarization. The longitudinal spin correlation shows a structure of
vortex-pairing in the transverse plane due to the convective flow of hot spots
in the radial direction. The dependence on colliding energy, rapidity,
centrality and sensitivity to the shear viscosity are also investigated.Comment: 5 pages in Latex, 3 figure
Effects of jet-induced medium excitation in -hadron correlation in A+A collisions
Coupled Linear Boltzmann Transport and hydrodynamics (CoLBT-hydro) is
developed for co-current and event-by-event simulations of jet transport and
jet-induced medium excitation (j.i.m.e.) in high-energy heavy-ion collisions.
This is made possible by a GPU parallelized (3+1)D hydrodynamics that has a
source term from the energy-momentum deposition by propagating jet shower
partons and provides real time update of the bulk medium evolution for
subsequent jet transport. Hadron spectra in -jet events of A+A
collisions at RHIC and LHC are calculated for the first time that include
hadrons from both the modified jet and j.i.m.e.. CoLBT-hydro describes well
experimental data at RHIC on the suppression of leading hadrons due to parton
energy loss. It also predicts the enhancement of soft hadrons from j.i.m.e. The
onset of soft hadron enhancement occurs at a constant transverse momentum due
to the thermal nature of soft hadrons from j.i.m.e. which also have a
significantly broadened azimuthal distribution relative to the jet direction.
Soft hadrons in the direction are, on the other hand, depleted due to
a diffusion wake behind the jet.Comment: 4 pages, 4 figures in LaTeX, final version published in PL
Effects of initial flow velocity fluctuation in event-by-event (3+1)D hydrodynamics
Hadron spectra and elliptic flow in high-energy heavy-ion collisions are
studied within a (3+1)D ideal hydrodynamic model with fluctuating initial
conditions given by the AMPT Monte Carlo model. Results from event-by-event
simulations are compared with experimental data at both RHIC and LHC energies.
Fluctuations in the initial energy density come from not only the number of
coherent soft interactions of overlapping nucleons but also incoherent
semi-hard parton scatterings in each binary nucleon collision. Mini-jets from
semi-hard parton scatterings are assumed to be locally thermalized through a
Gaussian smearing and give rise to non-vanishing initial local flow velocities.
Fluctuations in the initial flow velocities lead to harder transverse momentum
spectra of final hadrons due to non-vanishing initial radial flow velocities.
Initial fluctuations in rapidity distributions lead to expanding hot spots in
the longitudinal direction and are shown to cause a sizable reduction of final
hadron elliptic flow at large transverse momenta.Comment: 17 pages in RevTex, 18 figures, final version published in PR
A Two-Stage Conversion Process For Az31B Corrosion
Permanganate phosphate coating is considered as one of the most promising alternative coatings to chromate conversion coating because of the similarity between permanganate and chromate. However, the permanganate phosphate coating always has net-work cracks. In this paper, a thick and crack-free permanganate phosphate coating was developed by a two-stage conversion process. Results of scanning electron microscope (SEM) with X-ray diffraction (XRD) analysis showed that some more corrosion resistant compounds appeared in the coating after a two-stage conversion treatment, which were not found in the single conversion coating. Moreover, the two-stage conversion coating has a higher thickness with few cracks. Furthermore, electrochemical tests and salt spray test further exhibited that the two-stage conversion coating had a better corrosion performance than either of the two single conversion coatings
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