Title: The Physics of Non-Hydrodynamic Modes

Speaker: Paul Romatschke (CU Boulder)

Abstract: Examples for hydrodynamic collective modes are sound waves, shear and diffusive modes. But what are non-hydrodynamic collective modes? Most physicists likely have never ever heard about non-hydrodynamic modes in their entire career. Indeed, there does not seem to be a single textbook on this topic. This seminar will give an introduction to the physics of non-hydrodynamic modes, featuring gravitational waves, string theory predictions for experiment, cold atoms close to unitarity and heavy-ion collisions.

 

Title: A holographic view of the hydrodynamisation of quark-gluon plasma

Speaker: Wilke van der Schee (MIT)

Abstract: This talk aims to give an accessible introduction and overview of employing holography to better understand the creation of quark-gluon plasma in heavy ion collisions. Holography is a framework, originating from string theory, where it was realised that the dynamics of temperature and entropy present on black hole horizons is precisely described by certain infinitely strongly interacting quantum field theories. We will apply this framework in a setting where a black hole forms from two colliding `holographic nuclei’, and show that the resulting plasma is very quickly described by viscous relativistic hydrodynamics, a process now called hydrodynamisation. Lastly, we give some updates on recent extensions to Einstein-Gauss-Bonnet gravity, which can mimic quantum field theories with a finite coupling constant.

Title: Event-by-event hydrodynamics + jet energy loss: A solution to the RAA x  v2 puzzle

Speaker: Jorge Noronha (Sao Paolo)

Abstract: 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. A proper account of these event-by-event fluctuations in the soft sector, modeled via viscous hydrodynamics, combined with a jet energy loss model reveal that the positive contribution from low pT elliptic fluctuations overwhelms the negative contributions from event plane fluctuations, which leads to an enhancement of high pT elliptic flow in comparison to previous calculations. This provides a natural solution to the decade long RAA x v2 puzzle in heavy ion collisions. We also present the first theoretical calculation of high pT triangular flow, 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.

Title: Exploring The Dynamics Of Strongly Interacting Media With Dilepton Tomography

Speaker: Gojko Vuljanovic (OSU)

Abstract: Although rarely produced, electromagnetic (EM) probes provide direct insight into the new phase of matter produced in relativistic heavy-ion collisions: the Quark-Gluon Plasma (QGP). Lepton pairs (dileptons) radiated from the thermalized strongly-interacting medium are a class of EM probes that can isolate the thermal radiation from the early QGP phase of the medium. Indeed, QGP preferentially emits dileptons at high center of mass energy of the pairs (or high invariant mass), while low invariant mass dileptons originate from the late hadronic phase of medium. Having direct access to the QGP allows to investigate its dynamical properties using a 3+1D hydrodynamical simulation. Recently, much attention has been dedicated to the study of shear viscosity and its effects on the evolution of the medium created in heavy-ion collisions, through analyses of the hadronic final states. We show that thermal dileptons produced during Au-Au collisions at the top beam energy of the Relativistic Heavy Ion Collider (RHIC) give access to the temperature dependence of shear viscosity in the QGP phase, while also allowing to study the effects varying the relaxation time of shear viscous pressure on dilepton radiation. Furthermore, RHIC has published dilepton data from its Beam Energy Scan (BES) program, thus probing nuclear media at increasing net baryon densities. Through dilepton radiation, we examine the importance of baryon currents on the entire evolution of the medium.