Measurement of charge-dependent directed flow in STAR Beam Energy Scan (BES-II) Au+Au and U+U collisions

Abstract

We presented the rapidity dependence of directed flow ($v_1$) and its slope ($dv_1/dy$) for $\pi^\pm$, $K^\pm$ and $p(\bar{p}$) in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7 -- 19.6 GeV from the Beam Energy Scan Phase-II, as well as in U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV measured by the STAR experiment. The $v_1$ values are reported as a function of rapidity and centrality. Additionally, the $dv_1/dy$ and the charge dependent difference, $\Delta(dv_1/dy)$, of the three identified particles in U+U collisions is compared to those in Au+Au and isobar (Ru+Ru and Zr+Zr) collisions. These findings offer insights into the initial electromagnetic field as well as baryon transport at various system sizes and beam energies.