Date: March 16th, 2023

Speaker: Xiaoyu Liu (The Ohio State University)

Host: Zein-Eddine Meziani

Title: Measurement of Directed Flow at the STAR Experiment at RHIC

Abstract:

Directed flow (v1) describes the collective sideward motion of produced particles and nuclear fragments in heavy-ion collisions. The pseudorapidity (η) dependence of v1 can provide unique constraints on the initial conditions and dynamical evolution of the Quark Gluon Plasma (QGP). Directed flow in both spectator and participant regions is sensitive to early nonequilibrium dynamics and may provide insights into the baryon-stopping mechanism. In 2018, the Event Plane Detector (EPD, 2.1 < |η| < 5.1) was installed in STAR and used for the Beam Energy Scan phase-II (BES-II) data taking. The combination of EPD and high statistics BES-II data enables us to extend the v1 measurement to the forward and backward η regions, allowing us to verify the phenomenon of limiting fragmentation. In this talk, I will discuss the techniques for measuring v1 with a scintillator detector like EPD, present v1 over six units of η in Au+Au collisions at 27 GeV, and compare the results with the UrQMD model.