Bulletin of the American Physical Society
6th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Sunday–Friday, November 26–December 1 2023; Hawaii, the Big Island
Session 2WDA: Chirality and Vorticity IIIInvited Workshop
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Chair: Takafumi Niida Room: Hilton Waikoloa Village Kings 2 |
Sunday, November 26, 2023 2:00PM - 2:30PM |
2WDA.00001: Implications of directed flow and UPC measurements for electromagnetic and vorticity fields in heavy ion collisions Invited Speaker: Lijuan Ruan The electro-magnetic (EM) field generated by a moving heavy nucleus enables us to study many interesting emergent phenomena associated with EM field effects in heavy ion collisions. The time evolution of the EM field is still a hot topic for debate. Theoretical calculations indicate that charge dependent direct flow is sensitive to EM field effects. Experimentally multi-differential measurements of charge dependent direct flow have been made. In addition, dileptons from the photon-photon process in ultraperipheral heavy ion collisions (UPC) are sensitive to initial EM field. Similar measurements in peripheral to semi-central collisions have a potential to pin down possible final-state EM field. |
Sunday, November 26, 2023 2:30PM - 3:00PM |
2WDA.00002: Experimental status on spin polarization in heavy ion collisions at RHIC Invited Speaker: Kosuke Okubo In non-central collisions, large angular momentum can be manifested in the form of vorticity in the medium. Due to the spin-orbit coupling, spin directions of particles are aligned with the orbital angular momentum of the system. The global polarization of hyperons has been measured at various collision energies indicating the role of large angular momentum perpendicular to the reaction plane. In addition, the anisotropic flow of the medium can induce a local vorticity. It leads to spin polarization along the beam direction and might have different sensitivity to the relaxation time of the vorticity. The global spin alignment of vector meson can also offer information on the spin-orbit interactions of the QCD medium. In this talk, we will present recent measurements of the spin polarization of hyperons and spin alignment of vector mesons in heavy-ion collisions at RHIC. |
Sunday, November 26, 2023 3:00PM - 3:30PM |
2WDA.00003: Theoretical modeling of fluid vorticity and spin polarization Invited Speaker: Chun Shen Vorticity is a ubiquitous feature of collective properties of strongly-coupled fluid. Non-central heavy-ion collisions carry angular momenta of the order of 1,000 $hbar$ and can lead to a strong vortical structure inside the resulting Quark-Gluon Plasma (QGP) liquid. A local fluid rotation can induce a preferential orientation on the spins of the emitted particles through spin-orbit coupling. This talk summarizes the recent theoretical studies of $Lambda$ hyperon’s polarization observables with (3+1)D relativistic hydrodynamics in heavy-ion collisions. The effects of initial hot spot size and QGP’s specific shear viscosity on the polarization observables are quantified. We also examine the effects of the two formulations of the thermal shear tensor on the polarization observables using the same hydrodynamic background. With event-by-event simulations, we highlight new correlations among the Fourier coefficients of $Lambda$’s longitudinal polarization Pz and charged hadron anisotropic flow coefficients, which can further test the mapping from fluid velocity gradients to hyperon polarization. |
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