Papers Accepted for Publication in the Proceedings of QGPTH05
TALKS
Signs of thermalization from RHIC experiments
Authors:
Grazyna Odyniec
Comments: nucl-ex/0512009, 10 pages, 6 figures
Selected results from the first five years of RHIC data taking are reviewed
with emphasis on evidence for thermalization in central Au+Au collisions at
$\sqrt{s_{NN}}=200$ GeV.
Heavy quarks and heavy quarkonia as tests of thermalization
Authors:
J.L. Nagle (for the PHENIX Collaboration)
Comments: nucl-ex/0509024 8 pages, 5 figures
We present here a brief summary of new results on heavy quarks and heavy
quarkonia from the PHENIX experiment.
Strange quark collectivity of Phi meson at RHIC
Authors:
Y. G. Ma,
J. H. Chen,
G. L. Ma,
H. Z. Huang,
X. Z. Cai,
Z. J. He,
J. L. Long,
W. Q. Shen,
J. X. Zuo
Comments: nucl-th/0510095, 6 pages, 2 figures
Based on AMPT model, the elliptic flow $v_{2}$ of $\phi$ mesons which is
reconstructed from $K^{+}K^{-}$ at the Relativistic Heavy Ion Collider (RHIC)
energy has been studied. The results show that reconstructed $v_{2}$ of $\phi$
meson can keep the earlier information before $\phi$ decays and it seems to
obey the number of constituent quark scaling as other mesons and baryons. This
result indicates that the $\phi$ $v_2$ mostly reflects the parton level
collectivity developed during the early stage of the collisions and the strange
and light up/down quarks have similar azimuthal angular anisotropy properties
at the hadronization.
Formation of charmonium states in heavy ion collisions and
thermalization of charm
Authors: R. L. Thews
Comments: hep-ph/0511292, 8 pages, 5 figures
We examine the possibility to utilize in-medium charmonium formation in heavy
ion interactions at collider energy as a probe of the properties of the medium.
This is possible because the formation process involves recombination of charm
quarks which imprints a signal on the resulting normalized transverse momentum
distribution containing information about the momentum distribution of the
quarks. We have contrasted the transverse momentum spectra of J/Psi,
characterized by <p_T^2>, which result from the formation process in which the
charm quark distributions are taken at opposite limits with regard to
thermalization in the medium. The first uses charm quark distributions
unchanged from their initial production in a pQCD process, appropriate if their
interaction with the medium is negligible. The second uses charm quark
distributions which are in complete thermal equilibrium with the transversely
expanding medium, appropriate if a very strong interaction between charm quarks
and medium exists. We find that the resulting <p_T^2> of the formed J/Psi
should allow one to differentiate between these extremes, and that this
differentiation is not sensitive to variations in the detailed dynamics of
in-medium formation. We include a comparison of predictions of this model with
preliminary PHENIX measurements, which indicates compatibility with a
substantial fraction of in-medium formation.
What can we learn from hydrodynamic analysis at RHIC?
Authors:
Tetsufumi Hirano
Comments: nucl-th/0511036, 8 pages, 4 figures
We can establish a new picture, the perfect fluid sQGP core and the
dissipative hadronic corona, of the space-time evolution of produced matter in
relativistic heavy ion collisions at RHIC. It is also shown that the picture
works well also in the forward rapidity region through an analysis based on a
new class of the hydro-kinetic model and that this is a manifestation of rapid
increase of entropy density in the vicinity of QCD critical temperature, namely
deconfinement.
NeXSPheRIO results on elliptic flow at RHIC and connection with
thermalization
Authors:
R.Andrade,
F.Grassi,
Y.Hama,
T.Kodama,
O.Socolowski Jr.,
B.Tavares
Comments: nucl-th/0511021, 8 pages, 6 figures
Elliptic flow at RHIC is computed event-by-event with NeXSPheRIO. Reasonable
agreement with experimental results on $v_2(\eta)$ is obtained. Various effects
are studied as well: reconstruction of impact parameter direction, freeze out
temperature, equation of state (with or without crossover), emission mecanism.
Hints of incomplete thermalization in RHIC data
Authors:
Nicolas Borghini
Comments: nucl-th/0509092, 8 pages, 2 eps-figures
Report-no: CERN-PH-TH/2005-183
The large elliptic flow observed in Au-Au collisions at RHIC is often put
forward as a compelling evidence for the formation of a strongly-interacting
quark-gluon plasma. The main argument is that the measured elliptic flow is as
large as the value given by fluid-dynamics models that assume complete
thermalization. It is argued that this claim may not be justified, since a
detailed examination of experimental data rather suggests that the system
created is not fully equilibrated at the time when anisotropic flow develops.
Thermalization of gluons at RHIC: Dependence on initial conditions
Authors:
Zhe Xu,
Carsten Greiner
Comments: hep-ph/0511145, 8 pages, 4 figures
We investigate how thermalization of gluons depends on the initial conditions
assumed in ultrarelativistic heavy ion collisions at RHIC. The study is based
on simulations employing the pQCD inspired parton cascade solving the Boltzmann
equation for gluons. We consider independently produced minijets with $p_T >
p_0=1.3 \sim 2.0$ GeV and a color glass condensate as possible initial
conditions for the freed gluons. It turns out that full kinetic equilibrium is
achieved slightly sooner in denser system and its timescale tends to saturate.
Compared with the kinetic equilibration we find a stronger dependence of
chemical equilibration on the initial conditions.
Triple-gluon and triple-quark elastic scatterings and early
thermalization
Authors:
Xiao-Ming Xu
Comments: nucl-th/0510072 8 pages, 5 figures
Three-gluon to three-gluon scatterings lead to rapid thermalization of gluon
matter created in central Au-Au collisions at RHIC energies. Thermalization of
quark matter is studied from three-quark to three-quark scatterings.
Isotropization and thermalization in heavy ion collisions
Authors:
Yuri V. Kovchegov
Comments: hep-ph/0510232,
8 pages, 1 figure
We argue that isotropization and, consequently, thermalization of the system
of gluons and quarks produced in an ultrarelativistic heavy ion collision does
not follow from Feynman diagram analysis to any order in the coupling constant.
We conclude that the apparent thermalization of quarks and gluons, leading to
success of perfect fluid hydrodynamics in describing heavy ion collisions at
RHIC, can only be attributed to the non-perturbative QCD effects not captured
by Feynman diagrams.
We proceed by modeling these non-perturbative thermalization effects using
viscous hydrodynamics. We point out that matching Color Glass Condensate inital
conditions with viscous hydrodynamics leads to continuous evolution of all
components of energy-momentum tensor and, unlike the case of ideal
hydrodynamics, does not give a discontinuity in the longitudinal pressure. An
important consequence of such a matching is a relationship between the
thermalization time and shear viscosity: we observe that small viscosity leads
to short thermalization time.
A modified "bottom-up" thermalization in heavy ion collisions
Authors:
A.H. Mueller,
A.I. Shoshi,
S.M.H. Wong
Comments: hep-ph/0512045, 8 pages and 1 embedded figure
Report-no: CU-TP-1140
In the initial stage of the bottom-up picture of thermalization in heavy ion
collisions, the gluon distribution is highly anisotropic which can give rise to
plasma instability. This has not been taken account in the original paper. It
is shown that in the presence of instability there are scaling solutions, which
depend on one parameter, that match smoothly onto the late stage of bottom-up
when thermalization takes place.
Numerical studies of QGP instabilities and implications
Authors:
Guy D. Moore
Comments: hep-ph/0511203, 8 pages
Because the initial shape of the QGP in a heavy ion collision is anisotropic,
the momentum distribution becomes anisotropic after a short time. This leads to
plasma instabilities, which may help explain how the plasma isotropizes. We
explain the physics of instabilities and give the latest results of numerical
simulations into their evolution. Nonabelian interactions cut off the size to
which the soft unstable fields grow, and energy in the soft fields subsequently
cascades towards more ultraviolet scales. We present first results for the
power spectrum of this cascade.
Visualizing color plasma instabilities
Authors:
Michael Strickland
Comments: hep-ph/0511212, 10 pages, 5 figures. For full
resolution images see
this http URL
I discuss recent advances in the understanding of non-equilibrium gauge field
dynamics in plasmas which have particle distributions which are locally
anisotropic in momentum space. In contrast to locally isotropic plasmas such
anisotropic plasmas have a spectrum of soft unstable modes which are
characterized by exponential growth of transverse (chromo)-magnetic fields at
short times. The long-time behavior of such instabilities depends on whether or
not the gauge group is abelian or non-abelian. I will report on recent
numerical simulations which attempt to determine the long-time behavior of an
anisotropic non-abelian plasma within hard-loop effective theory. For novelty I
will present an interesting method for visualizing the time-dependence of SU(2)
gauge field configurations produced during our numerical simulations.
Numerical simulation of non-abelian particle-field dynamics
Authors:
Adrian Dumitru,
Yasushi Nara
Comments: hep-ph/0511242, 8 pages, 5 figures
Numerical 1D-3V solutions of the Wong-Yang-Mills equations with anisotropic
particle momentum distributions are presented. They confirm the existence of
plasma instabilities for weak initial fields and their saturation at a level
where the particle motion is affected, similar to Abelian plasmas. The
isotropization of the particle momenta by strong random fields is shown
explicitly, as well as their nearly exponential distribution up to a typical
hard scale, which arises from scattering off field fluctuations. By variation
of the lattice spacing we show that the effects described here are independent
of the UV field modes near the end of the Brioullin zone.
A Weibel instability in the melting Color Glass Condensate
Authors:
Paul Romatschke,
Raju Venugopalan
Comments: hep-ph/0510292, 8 pages
Report-no: BI-TP 2005/46
Based on hep-ph/0510121, we discuss further the numerical study of classical
SU(2) 3+1-D Yang-Mills equations for matter produced in a high energy heavy ion
collision. The growth of the amplitude of fluctuations as $\exp{(\Gamma
\sqrt{g^2\mu \tau})}$ (where $g^2\mu$ is a scale arising from the saturation of
gluons in the nuclear wavefunction) is shown to be robust over a wide range of
initial amplitudes that violate boost invariance. We argue that this growth is
due to a non-Abelian Weibel instability, the scale of which is set by a
dynamically generated plasmon mass. We find good agreement when we relate
$\Gamma$ to the prediction from kinetic theory.
Transport coefficients of strongly coupled gauge theories: insights from
string theory
Authors:
Andrei O. Starinets
Comments: nucl-th/0511073, 10 pages, 2 figures
The transport properties of certain strongly coupled thermal gauge theories
can be determined from their effective description in terms of gravity or
superstring theory duals. Here we provide a short summary of the results for
the shear and bulk viscosity, charge diffusion constant, and the speed of sound
in supersymmetric strongly interacting plasmas. We also outline a general
algorithm for computing transport coefficients in any gravity dual. The
algorithm relates the transport coefficients to the coefficients in the
quasinormal spectrum of five-dimensional black holes in asymptotically anti de
Sitter space.
Hawking-Unruh phenomenon in the parton
language
Authors: D. Kharzeev
Comments: 10 pages
Inelastic hadron interactions at high energies are
accompanied by a p ulse of a strong chromo--electric field. This field
leads to the decay of QCD vacuum which proceeds through the emission
of partons with a thermal spectrum. In a semi--classical treatment,
the effective temperature of the spectrum is determined by the
acceleration of partons in the classical chromo--electric field, in
accord with the general arguments given by Hawking and
Unruh.
Production of quark pairs from classical gluon fields
Authors:
F. Gelis,
K. Kajantie,
T. Lappi
Comments: hep-ph/0509363, 8 pages, 12 figures
We compute by numerical integration of the Dirac equation the number of
quark-antiquark pairs produced in the classical color fields of colliding
ultrarelativistic nuclei. Results for the dependence of the number of quarks on
the strength of the background field, the quark mass and time are presented. We
also perform several tests of our numerical method. While the number of qqbar
pairs is parametrically suppressed in the coupling constant, we find that in
this classical field model it could even be compatible with the thermal ratio
to the number of gluons.
Nonequilibrium quantum fields from first principles
Authors:
J. Berges,
Sz. Borsanyi
Comments: hep-th/0512010, 10 pages, 5 figures
Calculations of nonequilibrium processes become increasingly feasable in
quantum field theory from first principles. There has been important progress
in our analytical understanding based on 2PI generating functionals. In
addition, for the first time direct lattice simulations based on stochastic
quantization techniques have been achieved. The quantitative descriptions of
characteristic far-from-equilibrium time scales and thermal equilibration in
quantum field theory point out new phenomena such as prethermalization. They
determine the range of validity of standard transport or semi-classical
approaches, on which most of our ideas about nonequilibrium dynamics were based
so far. These are crucial ingredients to understand important topical phenomena
in high-energy physics related to collision experiments of heavy nuclei, early
universe cosmology and complex many-body systems.
Kinetic and chemical equilibration in scalar phi^4 theory
Authors:
Alejandro Arrizabalaga
Comments: hep-ph/0510407, 8 pages, 6 figures, uses axodraw
Approximations based on the 2PI effective action are used to investigate the
process of equilibration in phi^4 theory in 3+1 dimensions, both in the
symmetric and broken phase. A special emphasis is put on the study of the
kinetic and chemical equilibration.
Hadronization of expanding QGP
Authors:
J. Rafelski,
J. Letessier
Comments: nucl-th/0511016,
8 pages
We discuss how the dynamics of an exploding hot fireball of quark--gluon
matter impacts the actual phase transition conditions between the deconfined
and confined state of matter. We survey the chemical conditions prevailing at
hadronization.
Rapidity equilibration in d + Au and Au + Au systems
Authors:
Georg Wolschin
Comments: hep-ph/0509108, 10 pages, 4 figures
In a Relativistic Diffusion Model (RDM), the evolution of net-proton rapidity
spectra with sqrt(s_NN) in heavy systems is proposed as an indicator for local
equilibration and longitudinal expansion. The broad midrapidity valley recently
discovered at RHIC in central Au + Au collisions at sqrt(s_NN)= 200 GeV
suggests rapid local equilibration which is most likely due to deconfinement,
and fast longitudinal expansion. Rapidity spectra of produced charged hadrons
in d + Au and Au + Au systems at RHIC energies and their centrality dependence
are well described in a three-sources RDM. In central collisions, about 19 % of
the produced particles are in the equilibrated midrapidity region for d + Au.
The thermal model and the transition from baryonic to mesonic freeze-out
Authors:
J. Cleymans,
H. Oeschler,
K. Redlich,
S. Wheaton
Comments: hep-ph/0510283, 6 pages, 4 postscript figures
The present status of the thermal model is reviewed and the recently
discovered sharp peak in the $K^+/\pi^+$ ratio is discussed in this framework.
It is shown that the rapid change is related to a transition from a baryon
dominated hadronic gas to a meson dominated one. Further experimental tests to
clarify the nature of the transition are discussed. In the thermal model the
corresponding maxima in the Xi/pi and Omega/pi ratios occur at slightly
different beam energies.
The role of noise and dissipation in the hadronization of the
quark-gluon plasma
Authors:
Eduardo S. Fraga
Comments: hep-ph/0510344, 8 pages
We discuss the role of noise and dissipation in the explosive spinodal
decomposition scenario of hadron production during the chiral transition after
a high-energy heavy ion collision. We use a Langevin description inspired by
nonequilibrium field theory to perform real-time lattice simulations of the
behavior of the chiral fields. Preliminary results for the interplay between
additive and multiplicative noise terms, as well as for non-Markovian
corrections, are also presented.
POSTER CONTRIBUTIONS
Transverse energy and charged particle multiplicity at various
centralities at RHIC: Statistical model estimates
Authors:
Dariusz Prorok
Comments: hep-ph/0510402,
4 pages
The transverse energy and the charged particle multiplicity at midrapidity
are evaluated in a single-freeze-out model for different centrality bins at
RHIC at $\sqrt{s_{NN}}=130$ and 200 GeV. The predictions of the model are done
at the freeze-out parameters determined earlier from measured particle yields
and $p_{T}$ spectra. The results agree qualitatively well with the experimental
data.
Non-perturbative renormalization of Phi-derivable approximations in
theories with multiple fields
Authors:
U. Reinosa
Comments: hep-ph/0510380, 4 pages
We provide a renormalization procedure for Phi-derivable approximations in
theories coupling different types of fields. We illustrate our approach on a
scalar phi^4 theory coupled to fermions via a Yukawa-like interaction. The
non-perturbative renormalization amounts to fixing the scalar coupling via a
set of nested Bethe-Salpeter equations coupling fermions to scalars.
Anton Rebhan (rebhana at tph.tuwien.ac.at)
Last modified: Tue Jun 27 10:18:16 CEST 2006