Anisotropic flow in transport + hydrodynamics hybrid approaches
This contribution to the focus issue covers anisotropic flow in hybrid approaches. The historical development of hybrid approaches and their impact on the interpretation of flow measurements is reviewed. The major ingredients of a hybrid approach and the transition criteria between transport and hydrodynamics are discussed. The results for anisotropic flow in (event-by-event) hybrid approaches are presented. Some hybrid approaches rely on hadronic transport for the late stages for the reaction (so called afterburner) and others employ transport approaches for the early non-equilibrium evolution. In addition, there are ‘full’ hybrid calculations where a fluid evolution is dynamically embedded in a transport simulation. After demonstrating the success of hybrid approaches at high Relativistic Heavy Ion Collider and Large Hadron Collider energies, existing hybrid caluclations for collective flow observables at lower beam energies are discussed and remaining challenges outlined.

title: Collision Energy Evolution of Elliptic and Triangular Flow in a Hybrid Model
abstract: While the existence of a strongly interacting state of matter, known as 'quark-gluon plasma' (QGP), has been established in heavy ion collision experiments in the past decade, the task remains to map out the transition from the hadronic matter to the QGP. This is done by measuring the dependence of key observables (such as particle suppression and elliptic flow) on the collision energy of the heavy ions. This procedure, known as 'beam energy scan', has been most recently performed at the Relativistic Heavy Ion Collider (RHIC). Utilizing a Boltzmann+hydrodynamics hybrid model, we study the collision energy dependence of initial state eccentricities and the final state elliptic and triangular flow. This approach is well suited to investigate the relative importance of hydrodynamics and hadron transport at different collision energies.

title: Fully integrated transport approach to heavy ion reactions with an intermediate hydrodynamic stage
abstract: We present a coupled Boltzmann and hydrodynamics approach to relativistic heavy ion reactions. This hybrid approach is based on the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) transport approach with an intermediate hydrodynamical evolution for the hot and dense stage of the collision. Event-by-event fluctuations are directly taken into account via the nonequilibrium initial conditions generated by the initial collisions and string fragmentations in the microscopic UrQMD model. After a (3+1)-dimensional ideal hydrodynamic evolution, the hydrodynamical fields are mapped to hadrons via the Cooper-Frye equation and the subsequent hadronic cascade calculation within UrQMD proceeds to incorporate the important final state effects for a realistic freeze-out. This implementation allows us to compare pure microscopic transport calculations with hydrodynamic calculations using exactly the same initial conditions and freeze-out procedure. The effects of the change in the underlying dynamics--ideal fluid dynamics versus nonequilibrium transport theory--is explored. The freeze-out and initial state parameter dependencies are investigated for different observables. The time evolution of the baryon density and particle yields are also discussed. We find that the final pion and proton multiplicities are lower in the hybrid model calculation owing to the isentropic hydrodynamic expansion whereas the yields for strange particles are enhanced owing to the localmore » equilibrium in the hydrodynamic evolution. The results of the different calculations for the mean transverse mass excitation function, rapidity, and transverse mass spectra for different particle species at three different beam energies are discussed in the context of the available data.« less

title: Particlization in hybrid models
abstract: In hybrid models, which combine hydrodynamical and transport approaches to describe different stages of heavy-ion collisions, conversion of fluid to individual particles, particlization, is a non-trivial technical problem. We describe in detail how to find the particlization hypersurface in a 3+1 dimensional model, and how to sample the particle distributions evaluated using the Cooper-Frye procedure to create an ensemble of particles as an initial state for the transport stage. We also discuss the role and magnitude of the negative contributions in the Cooper-Frye procedure.

title: Directed and elliptic flow in heavy ion collisions at GSI-FAIR and CERN-SPS

title: Eccentricity fluctuations in an integrated hybrid approach: Influence on elliptic flow
abstract: of state and for averaged initial conditions or a full event-by-event setup are presented. These investigations allow the conclusion that in mid-central (b = 5‐9 fm) heavy-ion collisions the final elliptic flow is independent of the initial state fluctuations and the equation of state. Furthermore, it is demonstrated that most of the v2 is built up during the hydrodynamic stage of the evolution. Therefore, the use of averaged initial profiles does not contribute to the uncertainties of the extraction of transport properties of hot and dense QCD matter based on viscous hydrodynamic calculations.

title: Density of states in the K excitation spectra of solid and liquid lithium
abstract: Photoelectric yield measurements at the Li K edge and in an extended energy range 54-80 eV are presented. The sample temperature was varied in the range 79-480K (the liquid state). The edge consists of a steeply rising part due to the onset of transitions and a more slowly rising part which is interpreted as a rising density of states at the Fermi energy. With rising temperature the edge shifts to higher energy and broadens. Phonon broadening appears to contribute also at 79K to the width while the edge shape is consistent with a threshold exponent alpha 1 approximately=0. The structures in the range 54-80 eV are washed out on melting. These structures are well described by APW calculations by Bross (1973) of the optical density including plasmon damping.

title: Temperature Dependence of the K Absorption Edge of Lithium
abstract: The shape of the K absorption edge of Li has been measured at 293, 373, 443, and ∼480 K (liquid) by photoyield methods. Unpublished transmission data on the shape of the edge at and below room temperature have been reanalyzed. There is a marked increase of the width of the edge with increasing temperature above 293 K, indicating that the lattice plays a major role in the broadening of the edge.

title: LOST POWER INFLUENCE ON THE SYNCHROTRON ACCELERATING GAP. (IN GERMAN)