Directed flow of quarks from the RHIC Beam Energy Scan measured by STAR

Directed flow ($v_1$) is a good probe of the early-stage dynamics of collision systems, and the $v_1$ slope at midrapidity ($dv_1/dy|_{y=0}$) is sensitive to the system's equation of state. STAR has published $v_1(y)$ measurements for ten particle species ($\pi^\pm$, $p$, $\bar{p}$, $\Lambda$, $\bar{\Lambda}$, $\phi$, $K^\pm$ and $K^0_{S}$) in Au+Au collisions at eight beam energies from $\sqrt{s_{NN}} = 7.7$ GeV to 200 GeV. In this study, we employ a simple coalescence idea to decompose $v_1$ of hadrons into $v_1$ of constituent quarks. The $dv_1/dy$ values of $\bar{p}$, $K^-$ and $\bar{\Lambda}$ are used to test the coalescence sum rule for produced quarks. Data involving produced quarks support the coalescence picture at $\sqrt{s_{NN}} = 11.5$ GeV to 200 GeV, and a sharp deviation from this picture is observed at 7.7 GeV. The $dv_1/dy$ of transported quarks is studied via net particles (net $p$ and net $\Lambda$). In these proceedings, we further extract the $v_1$ slopes of produced and transported quarks, assuming that the coalescence sum rule is valid.Comment: 4 pages, 5 figures, Quark Matter 2018 proceeding

Theory of Side-Chain Liquid Crystal Polymers: Bulk Behavior and Chain Conformation

We study the thermodynamics and chain conformation of side-chain liquid crystal polymers (SCLCPs) in the bulk using the self-consistent-field approach and a new model to account for the coupling between the orientation of the side-chain liquid-crystal (LC) groups and that of the backbone segments. The new model accounts for both a global coupling between the polymer backbone and the nematic field and a local coupling between the polymer backbone and its attached LC group. Here, the terms global and local refer to the chemical (backbone) distance between the groups. A phenomenological parameter is introduced to represent the coupling strength and nature of the attachment, i.e., end-on vs side-on. The nematic field is shown to control the chain conformation through both the global and the local coupling effects. For the side-on SCLCPs, these two coupling effects act cooperatively so that the chain conformation is always prolate. For the end-on SCLCPs, these two effects act competitively. The chain conformation can be either oblate or prolate in this case, and depends on the relative strengths of these two couplings. On the other hand, the chain conformation also affects the nematic field, primarily through the global coupling. The prolate conformation enhances the nematic field and increases the phase transition temperature, whereas the oblate conformation frustrates the nematic field and decreases the transition temperature. The nematic order parameter is found to be determined mainly by the reduced temperature, and is not sensitive to the coupling effects. Furthermore, we show that the grafting density of the LC side groups has a significant effect on the chain conformation due to the orientational competition between the LC attached and unattached segments. For the end-on SCLCPs with lower graft density, the conformation of the chain backbone can be oblate at higher temperatures and prolate at lower temperatures, in agreement with the re-entrant nematic phase observed in experiments