### Conveners

#### Parallel: Initial conditions for hydrodynamics & transport coefficients

- Adrian Dumitru (Dept. of Natural Sciences, Baruch College (CUNY))

The applicability of hydrodynamical models in the extreme conditions produced in heavy ion collisions has not yet been properly understood theoretically. This happens mostly because the derivation of hydrodynamics from microscopic theory often relies on the assumption that the system is sufficiently close to equilibrium -- something difficult to justify in the rapidly expanding systems created...

The factorization breaking of collective flow in transverse momentum or in pseudorapidity is equivalent to a small decorrelation of flow in different phasespace regions. ATLAS has measured, besides the usual factorization breaking (including both flow magnitude and angle decorrelation), the flow angle decorrelation in pseudorapidity. The latter accounts for about half of the total...

The measurements of the flow phenomena in Xe+Xe and Pb+Pb collisions provide an excellent opportunity to study the interplay of viscous effects -- which diminish the azimuthal anisotropies more in Xe+Xe compared to Pb+Pb -- and initial geometry fluctuations which have an opposite effect. With the recently developed techniques, used for suppression of non-flow correlations in small systems,...

We study the longitudinal decorrelations of elliptic, triangular and quadrangular flows in heavy-ion collisions at the LHC and RHIC energies. The event-by-event CLVisc (3+1)-dimensional hydrodynamics model, combined with the fully fluctuating AMPT initial conditions, is utilized to simulate the space-time evolution of the strongly-coupled quark-gluon plasma. Detailed analysis is performed for...

Principal Component Analysis (PCA) is a mathematical tool that can capture the most important information in data. As one of the unsupervised algorithms of machine learning, PCA is good at discovering modes or hidden patterns in huge amount of data. It has seen successful applications of PCA in computer vision, data science and physics. Compared with deep learning algorithms, the advantage of...

We present a first-principles description of the primordial state of relativistic nucleus-nucleus collisions, whose density fluctuations and anisotropy we evaluate in the color glass condensate (CGC) framework of high-energy QCD. Relating the primordial anisotropy of the system in our approach to the measured final-state anisotropic flow through a simple linear mapping, we achieve an excellent...

Heavy quarks, owing to their large masses, are predominantly created in the initial hard scatterings in heavy-ion collisions. Therefore, they can play a crucial role in probing the initial-time dynamics in these collisions. Hydrodynamic model calculations suggest that the rapidity-odd directed flow ($v_{1}(y)$) of particles produced at mid-rapidity can originate from a tilt in the reaction...