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D. H. Rischke

Publications and source records attributed to D. H. Rischke.

46 records · Page 3Linked to original sources
arXiv1998

Collective dynamics in highly relativistic heavy-ion collisions

Hydrodynamics with cylindrical symmetry in transverse direction and longitudinal scaling flow is employed to calculate the transverse momentum spectra of various hadrons and clusters (e.g. pi, K, N, Phi, Lambda, d, He) in central heavy-ion collisions at CERN-SPS and BNL-RHIC energies up to pT=4 GeV. We discuss the sensitivity of these spectra with respect to the initial transverse density profile as well as to the choice of ``freeze-out'' hypersurface. For SPS energy and pT<2 GeV, overall good agreement of the pT distributions with data is found when freeze-out occurs along the T=130 MeV isotherm. Even high-pT neutral pion data can be described for a particular choice of the initial transverse density profile. It is shown that the average transverse velocity of heavy hadrons and hadronic clusters is a good measure for the collective flow velocity. The latter is found to be rather similar for SPS and RHIC energies, due to the ``stall'' of the flow within the long-lived mixed phase at RHIC. In case of thermalization and hydrodynamical expansion, the mean transverse momentum increases linearly with the hadron mass. In contrast, the string model FRITIOF7.02, which does not account for rescattering of secondary hadrons, predicts a strong dependence of on the quark composition of the hadron. Due to the different sensitivity to hard processes, hadrons with charm (anti-)quarks acquire significantly more transverse momentum than hadrons without c (or even without s) quarks.

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arXiv1997

Classical Gluon Radiation in Ultrarelativistic Nuclear Collisions: Space-Time Structure, Instabilities, and Thermalization

We investigate the space-time structure of the classical gluon field produced in an ultrarelativistic collision between color charges. The classical solution which was computed previously in a perturbative approach is shown to become unstable on account of the non-Abelian self-interaction neglected in the perturbative solution scheme. The time scale for growth of the instabilities is found to be of the order of the distance between the colliding color charges. We argue that these instabilities will eventually lead to thermalization of gluons produced in an ultrarelativistic collision between heavy nuclei. The rate of thermalization is estimated to be of order $g^2 μ$, where $g$ is the strong coupling constant and $μ^2$ the transverse color charge density of an ultrarelativistic nucleus.

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arXiv1997

Nonequilibrium fluid-dynamics in the early stage of ultrarelativistic heavy-ion collisions

To describe ultrarelativistic heavy-ion collisions we construct a three-fluid hydrodynamical model. In contrast to one-fluid hydrodynamics, it accounts for the finite stopping power of nuclear matter, i.e. for nonequilibrium effects in the early stage of the reaction. Within this model, we study baryon dynamics in the BNL-AGS energy range. For the system Au+Au we find that kinetic equilibrium between projectile and target nucleons is established only after a time $t_{CM}^{eq}\approx 5~fm/c\simeq 2R_{Au}/γ_{CM}$. Observables which are sensitive to the early stage of the collision (like e.g. nucleon flow) therefore differ considerably from those calculated in the one-fluid model.

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arXiv1996

Hot Spots and Turbulent Initial Conditions of Quark-Gluon Plasmas in Nuclear Collisions

As a result of multiple mini-jet production, initial conditions of the QCD plasma formed in ultrarelativistic nuclear collisions may be inhomogeneous, with large fluctuations of the local energy density (hot spots), and turbulent, with a chaotic initial transverse velocity field. Assuming rapid local thermalization, the evolution of such plasmas is computed using longitudinal boost-invariant 3+1-dimensional hydrodynamics. We compare the evolution in case that the speed of sound in the plasma is constant to one resulting from an equation of state involving a strong first order transition, with a minimum of the velocity of sound as a function of energy density. We find that azimuthally asymmetric fluctuations and correlations of the transverse energy flow can develop in both cases due to the initial inhomogeneities. Hot spots also enhance significantly high-transverse momenta direct photon yields. In the case with a phase transition, the hadronization surface evolves into an unusual foam-like structure. Also in that case, we find that hadronization is considerably delayed relative to the ideal gas case, just as previous studies have found for homogeneous initial conditions. The time-delay signature of a rapid cross-over transition region in the QCD equation of state (as observable via meson interferometry) is thus found to be remarkably robust to uncertainties in the initial conditions in heavy-ion reactions.

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arXiv1996

Transverse Shocks in the Turbulent Gluon Plasma Produced in Ultra-Relativistic A+A

Mini-jet production in ultra-relativistic nuclear collisions leads to initial conditions characterized by large fluctuations of the local energy density (hot spots) and of the collective flow field (turbulence). Assuming that local equilibrium is reached on a small time scale, $\sim 0.5$ fm/c, the transverse evolution of those initial conditions is computed using hydrodynamics. We find that a new class of collective flow phenomena (hadronic volcanoes) could arise under such conditions. This could be observable via enhanced azimuthal fluctuations of the transverse energy flow, $d^2E_\perp/dϕdy$.

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arXiv1996

Relativistic Hydrodynamics for Heavy--Ion Collisions: Freeze--Out and Particle Spectra

We investigate freeze--out in hydrodynamic models for relativistic heavy--ion collisions. In particular, instantaneous freeze--out across a hypersurface of constant temperature (``isothermal'' freeze--out) is compared with that across a hypersurface at constant time in the center-of-momentum frame (``isochronous'' freeze--out). For one--dimensional (longitudinal) expansion the rapidity distributions are shown to differ significantly in the two scenarios, while the transverse momentum spectra are remarkably similar. We also investigate the rapidity distribution in greater detail and show that the Gaussian-like shape of this distribution commonly associated with the Landau expansion model in general emerges only if one neglects contributions from time-like parts of the isothermal freeze--out hypersurface.

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arXiv1995

Thermal photons as a measure for the rapidity dependence of the temperature

The rapidity distribution of thermal photons produced in Pb+Pb collisions at CERN-SPS energies is calculated within scaling and three-fluid hydrodynamics. It is shown that these scenarios lead to very different rapidity spectra. A measurement of the rapidity dependence of photon radiation can give cleaner insight into the reaction dynamics than pion spectra, especially into the rapidity dependence of the temperature.

hep-ph↗
arXiv1994

Pion and thermal photon spectra as a possible signal for a phase transition

We calculate thermal photon and neutral pion spectra in ultrarelativistic heavy-ion collisions in the framework of three-fluid hydrodynamics. Both spectra are quite sensitive to the equation of state used. In particular, within our model, recent data for $S+Au$ at $200$ AGeV can only be understood if a scenario with a phase transition (possibly to a quark-gluon plasma) is assumed. Results for $Au+Au$ at $11$ AGeV and $Pb+Pb$ at $160$ AGeV are also presented.

hep-ph↗
arXiv1993

Finite Volume Effect of Nucleons and the Formation of the Quark-Gluon Plasma

We study a thermodynamically consistent implementation of the nucleon volume in the mean field theory, and find that this volume has large consequences on the properties of hadronic matter under extreme conditions such as in astrophysical objects and high energy heavy-ion collisions. It is shown that we can reproduce the critical temperature $T_{c}\simeq 200$ MeV predicted by lattice QCD calculations for the phase transition from hadronic matter to quark-gluon plasma, by using parameters which are adjusted to fit all empirical data for normal nuclear matter.

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