196 research outputs found
Transport coefficients of a unitarized pion gas
The latest experimental results in relativistic heavy-ion collisions show
that the matter there produced requires transport coefficients because of the
important collective properties found. We review the theoretical calculation of
these transport coefficients in the hadron side at low temperatures by
computing them in a gas composed of low energy pions. The interaction of these
pions is taken from an effective chiral theory and further requiring scattering
unitarity. The propagation of D and D* mesons in the thermalized pion gas is
also studied in order to extract the heavy quark diffusion coefficients in the
system.Comment: 7 pages, 3 figures, contribution to the International School of
Nuclear Physics, 33rd Course: From Quarks and Gluons to Hadrons and Nuclei,
Erice-Sicily: 16-24 September 201
Hydrodynamics and the Detection of the QCD Axial Anomaly in Heavy Ion Collisions
We consider the experimental implications of the axial current triangle
diagram anomaly in a hydrodynamic description of high density QCD. We propose a
signal of an enhanced production of spin-excited hadrons in the direction of
the rotation axis in off-central heavy ion collisions.Comment: 15 pages, 19 figures; v2: refs added, minor changes to the plots; v3,
comments adde
Flow fluctuations and long-range correlations: elliptic flow and beyond
These proceedings consist of a brief overview of the current understanding of
collective behavior in relativistic heavy-ion collisions. In particular, recent
progress in understanding the implications of event-by-event fluctuations have
solved important puzzles in existing data -- the "ridge" and "shoulder"
phenomena of long-range two-particle correlations -- and have created an
exciting opportunity to tightly constrain theoretical models with many new
observables.Comment: 10 pages, 2 figures, Proceedings for the 22nd International
Conference On Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter
2011), Annecy, France, May 23 - 28, 2011; includes Fig. 2 which was omitted
from journal submission for lack of spac
Universal parameterization of initial-state fluctuations and its applications to event-by-event anisotropy
We propose Elliptic Power and Power parameterizations for the probability
distribution of initial state anisotropies in heavy-ion collisions. By assuming
a linear eccentricity scaling, the new parameterizations can also be applied to
fluctuations of harmonic flow. In particular, we analyze flow multi-particle
cumulants and event-by-event distributions, both of which are recently measured
at the LHC.Comment: 4 pages and 3 figures, proceedings of the XXIV Quark Matter
conference, May 19-24 2014, Darmstadt (Germany
Two-component liquid model for the quark-gluon plasma
We consider a two-component-liquid model, a la Landau, for the quark-gluon
plasma. Qualitatively, the model fits well some crucial observations concerning
the plasma properties. Dynamically, the model assumes the existence of an
effective scalar field which is condensed. The existence of such a condensate
is supported by lattice data. We indicate a possible crucial test of the model
by lattice simulations.Comment: 5 pages; Talk given by V.I. Zakharov at 16th International Seminar on
High Energy Physics (QUARKS-2010), Kolomna, Russia, 6-12 June, 201
Hydrodynamic predictions for mixed harmonic correlations in 200 GeV Au+ Au collisions
Recent measurements at the Large Hadron Collider involve the correlation of different azimuthal flow
harmonics vn. These new observables add constraints to theoretical models and probe aspects of the system that
are independent of traditional single-harmonic measurements such as two-particle and multiparticle cumulants
vn{m}. Many of these new observables have not yet been measured at the Relativistic Heavy Ion Collider
(RHIC), leaving an opportunity to make predictions as a test of models across energies. We make predictions
using NEXSPHERIO, a hydrodynamical model which has accurately reproduced a large set of single-harmonic
correlations in a large range of transverse momenta and centralities at RHIC. Our predictions thus provide an
important baseline for comparison to correlations of flow harmonics, which contain nontrivial information about
the initial state as well as quark-gluon plasma transport properties. We also point out significant biases that
can appear when using wide centrality bins and nontrivial event weighting, necessitating care in performing
experimental analyses and in comparing theoretical calculations to these measurements
Charged particle directed flow in Pb-Pb collisions at sqrt{s_NN} = 2.76 TeV measured with ALICE at the LHC
Charged particle directed flow at midrapidity, |eta|<0.8, and forward
rapidity, 1.7 < |eta|<5.1, is measured in Pb-Pb collisions at sqrt{s_NN} = 2.76
TeV with ALICE at the LHC. Directed flow is reported as a function of collision
centrality, charged particle transverse momentum, and pseudo-rapidity. Results
are compared to measurements at RHIC and recent model calculations for LHC
energies.Comment: Talk given at the XXII International Conference on Ultrarelativistic
Nucleus-Nucleus Collisions (Quark Matter 2011), 23-28 May 2011, Annecy,
France; 4 pages, 3 figure
Elliptic flow in proton-proton collisions at 7 TeV
The angular correlations measured in proton-proton collisions at 7 TeV are
decomposed into contributions from back to back emission and elliptic flow.
Modeling the dominant term in the correlation functions as a momentum
conservation effect or as an effect of the initial transverse velocity of the
source, the remaining elliptic flow component can be estimated. The elliptic
flow coefficient extracted from the CMS Collaboration data is 0.04-0.08. No
additional small-angle, ridge-like correlations are needed to explain the
experimental data
Chiral restoration effects on the shear viscosity of a pion gas
We investigate the shear viscosity of a pion gas in relativistic kinetic
theory, using the Nambu-Jona-Lasinio model to construct the pion mass and the
pi-pi interaction at finite temperature. Whereas at low temperatures the
scattering properties and, hence, the viscosity are in agreement with
lowest-order chiral perturbation theory, we find strong medium modifications in
the crossover region. Here the system is strongly coupled and the scattering
lengths diverge, similarly as for ultra-cold Fermi gases at a Feshbach
resonance. As a consequence, the ratio eta/s is found to be strongly reduced as
compared to calculations without medium-modified masses and scattering
amplitudes. However, the quantitative results are very sensitive to the details
of the applied approximations.Comment: 15 pages, 12 figures; v2: extended discussions of the dressed sigma
propagator and the low-temperature limit, typos corrected, accepted versio
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