We discuss the information that can be deduced from a measurement of particle (hyperon or vector meson) polarization in ultrarelativistic nuclear collisions. We describe the sensitivity of polarization to initial conditions, hydrodynamic evolution and mean free path, and find that the polarization observable is sensitive to all details and stages of the system's evolution. We suggest that an experimental investigation covering production plane and reaction plane polarizations, as well as the polarization of jet-associated particles in the plane defined by the jet and particle direction, can help in disentangling the factors contributing to this observable. Scans of polarization in energy and rapidity might also point to a change in the system's properties.Comment: In press, Phys.Rev.C. One new figure, text streamlined and edited, physics conclusions and reasoning not change

This writeup is a compilation of the predictions for the forthcoming Heavy Ion Program at the Large Hadron Collider, as presented at the CERN Theory Institute ‘Heavy Ion Collisions at the LHC—Last Call for Predictions’, held from 14th May to 10th June 2007.

High pT > 10 GeV elliptic flow, which is experimentally measured via the correlation between soft and hard hadrons, receives competing contributions from event-by-event fluctuations of the low pT elliptic flow and event plane angle fluctuations in the soft sector. In this paper, a proper account of these event-by-event fluctuations in the soft sector, modeled via viscous hydrodynamics, is combined with a jet energy loss model to reveal that the positive contribution from low pT v2 fluctuations overwhelms the negative contributions from event plane fluctuations. This leads to an enhancement of high pT > 10 GeV elliptic flow in comparison to previous calculations and provides a natural solution to the decade long high pT RAA ⌦ v2 puzzle. We also present the first theoretical calculation of high pT v3, which is shown to be compatible with current LHC data. Furthermore, we discuss how short wavelength jet-medium physics can be deconvoluted from the physics of soft, bulk event-by-event flow observables using event shape engineering techniques.

We solve (3+1)-dimensional ideal hydrodynamical equations with source terms that describe punch-through and fully stopped jets in order to compare their final away-side angular correlations in a static medium. For fully stopped jets, the backreaction of the medium is described by a simple Bethe-Bloch-like model which leads to an explosive burst of energy and momentum (Bragg peak) close to the end of the jet's evolution through the medium. Surprisingly enough, we find that the medium's response and the corresponding away-side angular correlations are largely insensitive to whether the jet punches through or stops inside the medium. This result is also independent of whether momentum deposition is longitudinal (as generally occurs in pQCD energy loss models) or transverse (as the Bethe-Bloch formula implies). The existence of the diffusion wake is therefore shown to be universal to all scenarios where momentum as well as energy is deposited into the medium, which can readily be understood in ideal hydrodynamics through vorticity conservation. The particle yield coming from the strong forward moving diffusion wake that is formed in the wake of both punch-through and stopped jets largely overwhelms their weak Mach cone signal after freeze-out.

Recent data on the nuclear modification factor RAA of jet fragments in 2.76 ATeV Pb+Pb collisions at the Large Hadron Collider (LHC) indicate that the jet-medium coupling in a Quark-Gluon Plasma (QGP) is reduced at LHC energies and not compatible with the coupling deduced from data at the Relativistic Hadron Collider (RHIC). We estimate the reduction factor from a combined fit to the available data on RAA( √ s, pT , b) and the elliptic flow v2( √ s, pT , b) at √ s = 0.2, 2.76 ATeV over a transverse momentum range pT ∼ 10 − 100 GeV and a broad impact parameter, b, range. We use a simple analytic "polytrop" model (dE/dx = −κE a x z T c ) to investigate the dynamical jet-energy loss model dependence. Varying a = 0 − 1 interpolates between weakly-coupled and strongly-coupled models of jet-energy dependence while z = 0 − 2 covers a wide range of possible jet-path dependencies from elastic and radiative to holographic string mechanisms. Our fit to LHC data indicates an approximate 60% reduction of the coupling κ from RHIC to LHC and excludes energy-loss models characterized by a jet-energy exponent with a > 1/3. In particular, the rapid rise of RAA with pT ≥ 10 GeV combined with the slow variation of the asymptotic v2(pT ) at the LHC rules out popular exponential geometric optics models (a = 1). The LHC data are compatible with 0 ≤ a ≤ 1/3 pQCD-like energy-loss models where the jet-medium coupling is reduced by approximately 10% between RHIC and LHC.

The double-peak structure observed in soft-hard hadron correlations is commonly interpreted as a signature for a Mach cone generated by a supersonic jet interacting with the hot and dense medium created in ultrarelativistic heavy-ion collisions. We show that it can also arise due to averaging over many jet events in a transversally expanding background. We find that the jet-induced away-side yield does not depend on the details of the energy-momentum deposition in the plasma, the jet velocity, or the system size. Our claim can be experimentally tested by comparing soft-hard correlations induced by heavy-flavor jets with those generated by light-flavor jets.

We present the results of deriving the Israel-Stewart equations of relativistic dissipative fluid dynamics from kinetic theory via Grad's 14-moment expansion. Working consistently to second order in the Knudsen number, these equations contain several new terms which are absent in previous treatments.

We present the results of deriving the Israel-Stewart equations of relativistic dissipative fluid dynamics from kinetic theory via Grad's 14-moment expansion. Working consistently to second order in the Knudsen number, these equations contain several new terms which are absent in previous treatments.Comment: 7 pages, proceedings of the Erice School on Nuclear Physics "Heavy Ion collisions from the Coulomb Barrier up to the Quark Gluon Plasma", Erice, Sicily, Sep. 16 - 24, 200