Global variables and correlations: Summary of the results presented at the Quark Matter 2012 conference

Abstract

In these proceedings, we highlight recent developments from both theory and experiment related to the global description of matter produced in ultra-relativistic heavy-ion collisions as presented during the Quark Matter 2012 conference.

How (non-)linear is the hydrodynamics of heavy ion collisions?

“…The time-evolved fluctuation w (2) (τ , r) is determined from the full hydrodynamic evolution via Fourier analysis. 3 The main observation from Fig. 1 is that the fluid dynamic response to (5) The main message of this work is that even for the largest physically relevant amplitudes w (m) l , where non-linear contributions can dominate the hydrodynamic response, the observed non-linearities can be understood in terms of the perturbative ansatz (2).…”

“…In recent years, fluid dynamic simulations of relativistic heavy ion collisions have provided strong evidence for a picture according to which the momentum distributions of soft hadrons result from a fluid dynamic evolution of initial density fluctuations, see Refs. [1][2][3][4] for recent reviews. The research focuses now on understanding in detail the mapping from fluctuations in the initial state to experimentally accessible observables in the final state [5][6][7][8][9][10][11][12][13][14][15][16].…”

“…[19]. 3 Fluctuations at time τ 0 are cut-off in the region of very low background density, see e.g. w (2) (τ 0 , r) in Fig.…”

Freeze-out parameters from continuum extrapolation

“…Besides direct emissions, we can observe this matter at the point of break-up through the hadrons leaving the system. Prominent approaches include the hydrodynamical modelling of the angular distribution and the study of the event-by-event distribution of conserved charges [1].…”

Mode-by-mode hydrodynamics: Ideas and concepts

“…A background-fluctuation splitting and a Bessel-Fourier expansion for the fluctuating part of the hydrodynamical fields allows for a complete characterization of initial conditions, the fluid dynamical propagation of single modes, the study of interaction effects between modes, the determination of the associated particle spectra and the generalization of the whole program to event-by-event correlations and probability distributions.In recent years it has become apparent that what one may call the "fluid dynamic standard model of heavy ion collisions" according to which initial density anisotropies are evolved to final momentum anisotropies by almost ideal hydrodynamics works surprisingly well, see [1,2,3,4] for recent reviews. Some of the remaining puzzles are about the nature of the initial state directly after the collision and the early out-of-equilibrium dynamics that drives it towards local equilibrium on a rather short time scale, see [5] for an overview over recent literature on that question.…”