1,906 research outputs found
Dissipative Hydrodynamics and Heavy Ion Collisions
Recent discussions of RHIC data emphasized the exciting possibility that the
matter produced in nucleus-nucleus collisions shows properties of a
near-perfect fluid. Here, we aim at delineating the applicability of fluid
dynamics, which is needed to quantify the size of corresponding dissipative
effects. We start from the equations for dissipative fluid dynamics, which we
derive from kinetic theory up to second order (Israel-Stewart theory) in a
systematic gradient expansion. In model studies, we then establish that for too
early initialization of the hydrodynamic evolution (\tau_0 \lsim 1 fm/c) or
for too high transverse momentum (p_T \gsim 1 GeV) in the final state, the
expected dissipative corrections are too large for a fluid description to be
reliable. Moreover, viscosity-induced modifications of hadronic transverse
momentum spectra can be accommodated to a significant degree in an ideal fluid
description by modifications of the decoupling stage. We argue that these
conclusions, drawn from model studies, can also be expected to arise in
significantly more complex, realistic fluid dynamics simulations of heavy ion
collisions.Comment: 18 pages, 5 figures, uses revtex4; v2: references added, typos
correcte
Symmetry constraints for the emission angle dependence of Hanbury Brown--Twiss radii
We discuss symmetry constraints on the azimuthal oscillations of two-particle
correlation (Hanbury Brown--Twiss interferometry) radii for non-central
collisions between equal spherical nuclei. We also propose a new method for
correcting in a model-independent way the emission angle dependent correlation
function for finite event plane resolution and angular binning effects.Comment: 8 pages revtex4, 2 tables, no figures. Short Section VI added and
correction algorithm in Section VII made more explicit. Submitted to Physical
Review
Cyclic mutually unbiased bases, Fibonacci polynomials and Wiedemann's conjecture
We relate the construction of a complete set of cyclic mutually unbiased
bases, i. e., mutually unbiased bases generated by a single unitary operator,
in power-of-two dimensions to the problem of finding a symmetric matrix over
F_2 with an irreducible characteristic polynomial that has a given Fibonacci
index. For dimensions of the form 2^(2^k) we present a solution that shows an
analogy to an open conjecture of Wiedemann in finite field theory. Finally, we
discuss the equivalence of mutually unbiased bases.Comment: 11 pages, added chapter on equivalenc
Two-particle interferometry for non-central heavy-ion collisions
In non-central heavy ion collisions, identical two particle
Hanbury-Brown/Twiss (HBT) correlations C(K,q) depend on the azimuthal direction
of the pair momentum K. We investigate the consequences for a harmonic analysis
of the corresponding HBT radius parameters. Our discussion includes both, a
model- independent analysis of these parameters in the Gaussian approximation,
and the study of a class of hydrodynamical models which mimic essential
geometrical and dynamical properties of peripheral heavy ion collisions. Also,
we discuss the additional geometrical and dynamical information contained in
the harmonic coefficients of these HBT radius parameters. The leading
contribution of their first and second harmonics are found to satisfy simple
constraints. This allows for a minimal, azimuthally sensitive parametrization
of all first and second harmonic coefficients in terms of only two additional
fit parameters. We determine to what extent these parameters can be extracted
from experimental data despite finite multiplicity fluctuations and the
resulting uncertainty in the reconstruction of the reaction plane.Comment: 14 pages, RevTeX, 7 eps-figures include
The relationship between particle freeze-out distributions and HBT radius parameters
The relationship between pion and kaon space-time freeze-out distributions
and the HBT radius parameters in high-energy nucleus-nucleus collisions is
investigated. We show that the HBT radius parameters in general do not reflect
the R.M.S. deviations of the single particle production points. Instead, the
HBT radius parameters are most closely related to the curvature of the
two-particle space-time relative position distribution at the origin. We
support our arguments by studies with a dynamical model (RQMD 2.4).Comment: RevTex, 10 pages including 3 figures. v2: Discussion of the lambda
parameter has been added. PRC, in prin
Emission times and opacities from interferometry in non-central Relativistic Nuclear Collisions
The nuclear overlap zone in non-central relativistic heavy ion collisions is
azimuthally very asymmetric. By varying the angle between the axes of
deformation and the transverse direction of the pair momenta, the transverse
HBT radii oscillate in a characteristic way. It is shown that these
oscillations allow determination of source sizes, deformations as well as the
opacity and duration of emission of the source created in any non-central high
energy nuclear collisions. The behavior of the physical quantities with
centrality of the collisions is discussed --- in particular changes caused by a
possible phase transition to a quark-gluon plasma.Comment: Revised version, to appear in Phys. Rev. Letter
Flow effects on the freeze-out phase-space density in heavy ion collisions
The strong longitudinal expansion of the reaction zone formed in relativistic
heavy-ion collisions is found to significantly reduce the spatially averaged
pion phase-space density, compared to naive estimates based on thermal
distributions. This has important implications for data interpretation and
leads to larger values for the extracted pion chemical potential at kinetic
freeze-out.Comment: 5 pages, 3 figures included via epsfig, added discussion of different
transverse density profiles, 1 new figur
Event Anisotropy in High Energy Nucleus-Nucleus Collisions
The predictions of event anisotropy parameters from transport model RQMD are
compared with the recent experimental measurements for 158 GeV Pb+Pb
collisions. Using the same model, we study the time evolution of event
anisotropy at 2 GeV and 158 GeV for several colliding systems. For the
first time, both momentum and configuration space information are studied using
the Fourier analysis of the azimuthal angular distribution. We find that, in
the model, the initial geometry of the collision plays a dominant role in
determining the anisotropy parameters.Comment: 18 pages, 7 figures, 2 table
On the Evolution of Ion Bunch Profile in the Presence of Longitudinal Coherent Electron Cooling
In the presence of longitudinal coherent electron cooling, the evolution of
the line-density profile of a circulating ion bunch can be described by the 1-D
Fokker-Planck equation. We show that, in the absence of diffusion, the 1-D
equation can be solved analytically for certain dependence of cooling force on
the synchrotron amplitude. For more general cases with arbitrary diffusion, we
solved the 1-D Fokker-Planck equation numerically and the numerical solutions
have been compared with results from macro-particle tracking
Heavy ion collisions and AdS/CFT
We review some recent applications of the AdS/CFT correspondence to heavy ion
collisions including a calculation of the jet quenching parameter in N=4
super-Yang-Mills theory and quarkonium suppression from velocity scaling of the
screening length for a heavy quark-antiquark pair. We also briefly discuss
differences and similarities between QCD and N=4 Super-Yang-Mills theory.Comment: Plenary talk given at Quark Matter 2006, Shanghai, China, 14-20 Nov
2006; to appear in the conference proceedin
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