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Ulrich W. Heinz

Publications and source records attributed to Ulrich W. Heinz.

69 records · Page 4Linked to original sources
arXiv2005

Dissipative hydrodynamics for viscous relativistic fluids

Explicit equations are given for describing the space-time evolution of non-ideal (viscous) relativistic fluids undergoing boost-invariant longitudinal and arbitrary transverse expansion. The equations are derived from the second-order Israel-Stewart approach which ensures causal evolution. Both azimuthally symmetric (1+1)-dimensional and non-symmetric (2+1)-dimensional transverse expansion are discussed. The latter provides the formal basis for the hydrodynamic computation of elliptic flow in relativistic heavy-ion collisions including dissipative effects.

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arXiv2005

Multiplicity distribution and source deformation in full-overlap U+U collisions

We present a full Monte Carlo simulation of the multiplicity and eccentricity distributions in U+U collisions at sqrt(s) = 200 A GeV. While unavoidable trigger inefficiencies in selecting full-overlap U+U collisions cause significant modifications of the multiplicity distribution shown in PRL94, 132301 (2005), a selection of source eccentricities by cutting the multiplicity distribution is still possible.

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arXiv2005

Equation of State and Collective Dynamics

This talk summarizes the present status of a program to quantitatively relate data from the Relativistic Heavy Ion Collider (RHIC) on collective expansion flow to the Equation of State (EOS) of hot and dense strongly interacting matter, including the quark-gluon plasma and the quark-hadron phase transition. The limits reached with the present state of the art and the next steps required to make further progress will both be discussed.

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arXiv2004

Projected Three-Pion Correlation Functions

We propose a new procedure for constructing projected three-pion correlation functions which reduces undesirable artificial momentum dependences resulting from the commonly used procedure and facilitates comparison of three-pion correlation data with theoretical models.

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arXiv2004

Concepts of Heavy-Ion Physics

In these lectures I present the key ideas driving the field of relativistic heavy-ion physics and develop some of the theoretical tools needed for the description and interpretation of heavy-ion collision experiments.

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arXiv2004

Thermalization at RHIC

Ideal hydroynamics provides an excellent description of all aspects of the single-particle spectra of all hadrons with transverse momenta below about 1.5-2 GeV/c at RHIC. This is shown to require rapid local thermalization at a time scale below 1 fm/c and at energy densities which exceed the critical value for color deconfinement by an order of magnitude. The only known thermalized state at such energy densities is the quark-gluon plasma (QGP). The rapid thermalization indicates that the QGP is a strongly interacting liquid rather than the weakly interacting gas of quarks and gluons that was previously expected.

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arXiv2003

Emission angle dependence of HBT radii: Theoretical background and interpretation

The Wigner function formalism which relates source size parameters to experimental ``HBT radii'' extracted from two-particle Bose-Einstein correlations is generalized to azimuthally deformed and longitudinally tilted sources. It is explained how this can be used to complement anisotropic flow measurements with relevant space-time information on the source.

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arXiv2002

The quark-gluon plasma at RHIC

I present a theory-guided review of RHIC data, arguing that they provide strong evidence for formation of a thermalized quark-gluon plasma at RHIC. Strong radial flow reflects high thermal pressure in the reaction zone. Large elliptic flow proves that the pressure builds up quickly and the system thermalizes on a very short time scale of less than 1 fm/c. The observed hadron yields are consistent with statistical hadron formation from a quark-gluon plasma, followed by immediate chemical decoupling due to strong radial expansion. The observed suppression of jets appears to confirm the predicted large energy loss suffered by hard partons moving through a quark-gluon plasma; more work is required to quantitatively understand this effect. Source size measurements using two-particle correlations do not seem to fit into this picture; the origin of this discrepancy (``HBT puzzle'') is presently not understood.

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arXiv2002

Emission angle dependent pion interferometry at RHIC and beyond

We use hydrodynamics to generate freeze-out configurations for non-central heavy-ion collisions at present and future collider energies. Such collisions are known to produce strong elliptic flow. The accompanying space-time structure of the source at freeze-out is analyzed using pion interferometry. Between RHIC and LHC energies the source deformation in the transverse plane changes sign. This leaves characteristic signatures in the emission angle dependence of the HBT radii.

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arXiv2002

Shear viscosity of hot scalar field theory in the real-time formalism

Within the closed time path formalism a general nonperturbative expression is derived which resums through the Bethe-Salpter equation all leading order contributions to the shear viscosity in hot scalar field theory. Using a previously derived generalized fluctuation-dissipation theorem for nonlinear response functions in the real-time formalism, it is shown that the Bethe-Salpeter equation decouples in the so-called (r,a) basis. The general result is applied to scalar field theory with pure lambda*phi**4 and mixed g*phi**3+lambda*phi**4 interactions. In both cases our calculation confirms the leading order expression for the shear viscosity previously obtained in the imaginary time formalism.

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arXiv2002

Two RHIC puzzles: Early thermalization and the HBT problem

Hadron spectra from the first year RHIC run are shown to be excellently reproduced by hydrodynamic calculations. We argue that in particular the elliptic flow data provide strong evidence for early thermalization at RHIC, at energy densities well above deconfinement, but that the phenomenologically extracted short thermalization time scale of less than 1 fm/c provides a serious challenge for theory. The HBT radii from the hydrodynamic calculations agree only qualitatively with the data, showing significant quantitative discrepancies. It is argued that this points to a still incomplete understanding of the freeze-out process at RHIC.

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arXiv2001

Early thermalization at RHIC

It is shown that recent RHIC data on hadron spectra and elliptic flow can be excellently reproduced within a hydrodynamic description of the collision dynamics, and that this provides strong evidence for rapid thermalization while the system is still in the quark-gluon plasma phase. But even though the hydrodynamic approach provides an impressive description of the single-particle momentum distributions, it fails to describe the two-particle momentum correlation (HBT) data for central Au+Au collisions at RHIC. We suggest that this is not likely to be repaired by further improvements in our understanding of the early collision stages, but probably requires a better modelling of the freeze-out process. We close with a prediction of the phases of the azimuthal oscillations of the HBT radii in noncentral collisions at RHIC.

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arXiv2001

From SPS to RHIC: Breaking the Barrier to the Quark-Gluon Plasma

After 15 years of heavy-ion collision experiments at the AGS and SPS, the recent turn-on of RHIC has initiated a new stage of quark-gluon plasma studies. I review the evidence for deconfined quark-gluon matter at SPS energies and the recent confirmation of some of the key ideas by the new RHIC data. Measurements of the elliptic flow at RHIC provide strong evidence for efficient thermalization during the very early partonic collision stage, resulting in a well-developed quark-gluon plasma with almost ideal fluid-dynamical collective behaviour and a lifetime of several fm/c.

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