Quark Matter 2018

Directed Flow Due to the Initial Source Tilt and Density Asymmetry in Cu+Au and Au+Au Collisions at STAR

15 May 2018, 17:00

2h 40m

First floor and third floor (Palazzo del Casinò)

Poster Initial state physics and approach to equilibrium Poster Session

Speaker

Takafumi Niida (Wayne State University)

Description

Despite of a generally very successful description of the elliptic and higher harmonic flow in heavy-ion collisions by theoretical models, there is no single model that explains the dependence of the directed flow on pseudorapidity, collision energy, system size, and the particle type. This indicates that an important piece in our picture of ultrarelativistic heavy-ion collisions is still missing. Directed flow is thought to arise from two main mechanisms: the so-called "tilted" source and the dipole-like initial density asymmetry. The asymmetric Cu+Au collisions provide a unique possibility to identify the roles of theses two mechanisms.

We present the results of directed flow measurements for charged and identified particles in Cu+Au and Au+Au collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}$ = 200 GeV as a function of centrality, pseudorapidity, and transverse momentum. We show how the comparison of pseudorapidiy dependence of $v_1$ and $⟨p_x⟩$ can be used to quantify the contribution of different mechanisms of directed flow formation. We compare the results with Pb+Pb collisions at the LHC energies, and discuss the centrality and energy dependence of the relative contributions to the directed flow from the initial source tilt and from the density asymmetry.

Presentation materials

QM18_poster_niida_v3.pdf