120 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
Bayesian extraction of jet energy loss distributions in heavy-ion collisions
Based on the factorization in perturbative QCD, a jet cross sections in
heavy-ion collisions can be expressed as a convolution of the jet cross section
in collisions and a jet energy loss distribution. Using this simple
expression and the Markov Chain Monte Carlo method, we carry out Bayesian
analyses of experimental data on jet spectra to extract energy loss
distributions for both single inclusive and -triggered jets in
collisions with different centralities at two colliding energies at the Large
Hadron Collider. The average jet energy loss has a dependence on the initial
jet energy that is slightly stronger than a logarithmic form and decreases from
central to peripheral collisions. The extracted jet energy loss distributions
with a scaling behavior in have a
large width. These are consistent with the linear Boltzmann transport model
simulations, in which the observed jet quenching is caused on the average by
only a few out-of-cone scatterings.Comment: 5 pages in RevTex, 3 figures, final version to appear in Phys. Rev.
Letter
Gradient Tomography of Jet Quenching in Heavy-Ion Collisions
Transverse momentum broadening and energy loss of a propagating parton are
dictated by the space-time profile of the jet transport coefficient in
a dense QCD medium. The spatial gradient of perpendicular to the
propagation direction can lead to a drift and asymmetry in parton transverse
momentum distribution. Such an asymmetry depends on both the spatial position
along the transverse gradient and path length of a propagating parton as shown
by numerical solutions of the Boltzmann transport in the simplified form of a
drift-diffusion equation. In high-energy heavy-ion collisions, this asymmetry
with respect to a plane defined by the beam and trigger particle (photon,
hadron or jet) with a given orientation relative to the event plane is shown to
be closely related to the transverse position of the initial jet production in
full event-by-event simulations within the linear Boltzmann transport model.
Such a gradient tomography can be used to localize the initial jet production
position for more detailed study of jet quenching and properties of the
quark-gluon plasma along a given propagation path in heavy-ion collisions.Comment: 5 pages in RevTex with 4 figures, final published version in PR
Exploring QCD matter in extreme conditions with Machine Learning
In recent years, machine learning has emerged as a powerful computational
tool and novel problem-solving perspective for physics, offering new avenues
for studying strongly interacting QCD matter properties under extreme
conditions. This review article aims to provide an overview of the current
state of this intersection of fields, focusing on the application of machine
learning to theoretical studies in high energy nuclear physics. It covers
diverse aspects, including heavy ion collisions, lattice field theory, and
neutron stars, and discuss how machine learning can be used to explore and
facilitate the physics goals of understanding QCD matter. The review also
provides a commonality overview from a methodology perspective, from
data-driven perspective to physics-driven perspective. We conclude by
discussing the challenges and future prospects of machine learning applications
in high energy nuclear physics, also underscoring the importance of
incorporating physics priors into the purely data-driven learning toolbox. This
review highlights the critical role of machine learning as a valuable
computational paradigm for advancing physics exploration in high energy nuclear
physics.Comment: 146 pages,53 figure
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