Initial State Fluctuations and Final State Correlations in Relativistic Heavy-Ion Collisions
We review the phenomenology and theory of bulk observables in ultra- relativistic heavy-ion collisions, focussing on recent developments involving event-by- event uctuations in the initial stages of a heavy ion collision, and how they manifest in observed correlations. We rst dene the relevant observables and show how each measurement is related to underlying theoretical quantities. Then we review the prevailing picture of the various stages of a collision, including the state-of-the-art modeling of the initial stages of a collision and subsequent hydrodynamic evolution, as well as hadronic scattering and freeze-out in the later stages. We then discuss the recent results that have shaped our current understanding and identify the challenges that remain. Finally, we point out open issues and the potential for progress in the eld.

title: Longitudinal flow and onset of deconfinement
abstract: The effects of the onset of deconfinement on longitudinal and transverse flow are studied. First, we analyze longitudinal pion spectra from $E_{\rm lab}= 2A$ GeV to $\sqrt{s_{\rm NN}}=200$ GeV within Landau's hydrodynamical model and the UrQMD transport approach. From the measured data on the widths of the pion rapidity spectra, we extract the sound velocity $c_s^2$ in the early stage of the reactions. It is found that the sound velocity has a local minimum (indicating a softest point in the equation of state, EoS) at $E_{\rm beam}=30A$ GeV. This softening of the EoS is compatible with the assumption of the formation of a mixed phase at the onset of deconfinement. Furthermore, the energy excitation function of elliptic flow ($v_2$) from $E_{\rm beam}=90A$ MeV to $\sqrt{s_{\rm NN}}=200$ GeV is explored within the UrQMD framework and discussed in the context of the available data. The transverse flow should also be sensitive to changes in the equation of state. Therefore, the underestimation of elliptic flow by the UrQMD model calculation above $E_{\rm lab}= 30A$ GeV might also be explained by assuming a phase transition from a hadron gas to the quark gluon plasma around this energy. This would be consistent with the model calculations, indicating a transition from hadronic matter to ``string matter'' in this energy range.

title: Initial-state fluctuations at the RHIC and the LHC in event-by-event ideal hydrodynamics
abstract: Triangular flow is a new observable in heavy ion collisions that provides interesting information about the structure of the initial state that enters (viscous) hydrodynamic simulations. The longitudinal correlations of the initial state triangularity is investigated to evaluate the potential to distinguish different energy deposition scenarios. We find that radiation processes in a parton cascade introduce similar longitudinal structures as the string fragmentation processes in a hadron cascade. The weak centrality dependence of triangular flow is reproduced within an event-by-event hybrid approach and confirms its sensitivity to initial state fluctuations. The transverse momentum-dependent triangular flow of identified particles at LHC energies is predicted and shows a mass splitting similar to the one observed for elliptic flow.

title: What the collective flow excitation function can tell about the quark–gluon plasma
abstract: Recent STAR data from the RHIC beam energy scan (BES) show that the slope of the net-proton directed flow v 1 at midrapidity changes sign twice within the collision energy range 7.7–39 GeV. To investigate this phenomenon, we study the collision energy dependence of v 1 utilizing a hybrid model which combines Boltzmann transport and hydrodynamic approach. Calculations with dynamically evolved initial and final state show no qualitative difference between an equation of state with a cross-over and one with a first-order phase transition, in contrast to earlier pure fluid predictions. Our analysis of the elliptic flow v 2 shows that pre-equilibrium transport dynamics are partially compensating for the diminishing contribution to the elliptic flow from the hydrodynamical phase at lower energies, which leads to a qualitative agreement with STAR BES results in midcentral collisions. No compensation from transport is found for integrated v 3 , which decreases from ≈0.02 at s N N = 27 GeV to ≈0.005 at s N N = 7.7 GeV in midcentral collisions.

title: UrQMD v2.3: Changes and Comparisons
abstract: The new version of the Ultra-relativistic Quantum Molecular Dynamics model (UrQMD-2.3) is presented. The Ultra-relativistic Quantum Molecular Dynamics model (UrQMD) is a microscopic many body approach to pp, pA and AA interactions at relativistic energies. The major updates and changes are explained and a comparison to the previous version (UrQMD-1.3p1) in the context of the available data is performed. The plots and numerical data tables for hadron (i.e. $\pi$, K, p, $\bar{p}$, $\Lambda$, $\bar{\Lambda}$, $\Xi$, $\bar{\Xi}$, $\Omega$, $\bar{\Omega}$) multiplicities, and mean transverse mass momenta, $ -m_0$ excitation functions, transverse mass spectra and rapidity distributions in pp and central Au+Au/Pb+Pb reactions from $E_{\rm lab}=2A $GeV to $\sqrt{s}_{\rm NN}=200$ GeV are provided in this paper. The source code of UrQMD-2.3 is available at this http URL

title: Anisotropic flow in transport + hydrodynamics hybrid approaches
abstract: 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: Damping antennas for spurious RF-modes in electron-positron storage rings
abstract: The maximum beam currents in DORIS were limited mainly by instabilities induced by the rf-cavities. To overcome this difficulty, the higher cavity modes must be damped. Special damping antennas were developed for this purpose.

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: 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.