UCLA

At lower RHIC energies, hadronization in the quark–gluon-plasma (QGP) fireball is significantly influenced by transported quarks carried in from the colliding nuclei. Within the quark coalescence picture, these transported quarks, which experience the full evolution of the system’s pressure gradients, imprint distinct flavor and dynamical signatures on final-state hadrons. This thesis presents three complementary measurements from the STAR Beam Energy Scan Phase II (BES-II) program in Au+Au collisions.The influence of transported quarks is directly reflected in the elliptic flow (v2) of charged pions. In Au+Au collisions at √ sNN = 7.7–27 GeV, π − carries systematically larger v2 than π + across centralities and energies, consistent with the higher availability of transported d quarks relative to u quarks in the neutron-rich Au nucleus. Using a coalescence sum rule with the antiproton as a proxy for the produced-quark flow, the transported quark ratio Ntr d /Ntr u is extracted and found to be consistent with the Au stoichiometric value 315/276 ≈ 1.14, providing a direct link between the quark content of the colliding nuclei, via nuclear geometry, and the final collective expansion of the QGP drop.Electromagnetic fields generated by the spectator protons in peripheral collisions offer a complementary window into the quark-level response at hadronization. The directed flow (v1) splitting between Λ 0 and Λ¯ 0 is measured over the same BES-II energy range; the slope difference ∆(dv1/dy) becomes negative in peripheral collisions, mirroring the behavior previously observed for charged hadrons and attributed to the combined Faraday and Coulomb effects. A first-order coalescence test using p–p¯, supplemented by a second-order correction based on K+–K−, supports the coalescence picture and indicates that the electromagnetic response acts at the level of the constituent quarks and is not set by electric charge alone.These flow-based analyses probe the transported-quark coalescence picture through anisotropic momentum signatures. A more direct handle on the transported-baryon population is provided by the Ω − hyperon: at √ sNN = 7.7–27 GeV, the Ω − yield carries a substantial excess over Ω¯ + from baryon transport. We establish the Combinatorial Background Subtraction (CBS) correlation method, which uses associated kaons to decompose the Ω − population into its transported and pair-produced components and to probe whether their hadronization signatures differ. At √ sNN = 19.6 GeV, the transported Ω − shows a modest excess of associated kaons over a pair-produced Ω, 1.10±0.74 per Ω, in the direction expected if its strangeness is balanced by kaons rather than by co-produced anti-baryons.