Speaker
Dr
Subhash Singha
(Kent State University)
Description
A goal of the research at the Relativistic Heavy Ion Collider (RHIC) is to explore deconfined quark-gluon matter. Directed flow ($v_{1}$) is one observable that is sensitive to the dynamics of the system at early times of the collisions. Model calculations have indicated that the $v_{1}$-slope ($dv_1/dy$) at mid-rapidity is sensitive to the Equation of State (EoS) of the system. STAR has taken data over a wide range of beam energies (7.7 - 200~GeV) to explore the QCD phase diagram. Measurements of the beam energy dependence of $dv_1/dy$ for protons and net-protons near mid-rapidity have been interpreted in the literature as favoring a softening of the QCD EoS around $\sqrt{s_{\rm NN}}$ = 10 - 20~GeV. $v_1$ measurements with different hadron species can help disentangle the roles of produced quarks versus those transported from the initial nuclei. Moreover these measurements allow us to investigate the $v_{1}$ pattern of the constituent quarks. Recently, it was predicted that the transient magnetic field in heavy-ion collisions can induce a larger $v_1$ for heavy quarks than for light quarks. The model calculation also suggested that the sign of $dv_1/dy$ at mid-rapidity is opposite for charm $(c)$ and anti-charm ($\bar{c}$) quarks. This argues for heavy quark $v_1$ measurement being a new approach to study the initial electromagnetic field. The Heavy Flavor Tracker (HFT) in STAR has demonstrated an excellent performance in reconstructing $D^{0} (\bar{u}c)$ and $\overline{D^0} (u\bar{c})$ via hadronic decay channels.
We will report results of $v_1$ and $dv_1/dy$ near mid-rapidity for $\pi^{\pm}$, $K^{\pm}$, $K_s^0$, $p$, $\bar{p}$, $\Lambda$, $\bar{\Lambda}$ and $\phi$ in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 7.7 - 200~GeV, and for $D^{0}$ and $\overline{D^{0}}$ at $\sqrt{s_{\rm NN}}$ = 200~GeV. The results will be compared with recent theoretical calculations and the physics implications will be discussed.
Author
Dr
Subhash Singha
(Kent State University)
