922 research outputs found
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
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
The non-Abelian feature of parton energy loss in energy dependence of jet quenching in high-energy heavy-ion collisions
One of the non-Abelian features of parton energy loss is the ratio between gluon and quark jets. Since jet production rate is
dominated by quark jets at high and by gluon jets at low
, high hadron suppression in high-energy heavy-ion collisions should
reflect such a non-Abelian feature. Within a leading order perturbative QCD
parton model that incorporates transverse expansion and Woods-Saxon nuclear
distribution, the energy dependence of large GeV/ hadron
suppression is found to be sensitive to the non-Abelian feasture of parton
energy loss and could be tested by data from low energy runs at RHIC or data
from LHC.Comment: RevTex 4, 7 pages, 3 figure
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
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