Speaker
Description
The shape and orientation of colliding nuclei play a crucial role in determining the initial conditions of the quark-gluon plasma (QGP), which influence key observables such as anisotropic and radial flow. In this talk, we present the measurements of $v_n$, $p_{\rm T}$ fluctuation, and $v_n-p_{\rm T}$ correlations in isobar-like $^{238}$U+$^{238}$U and $^{197}$Au+$^{197}$Au collisions at $\sqrt{s_{\rm NN}}=$ 193 and 200 GeV, respectively. Our results reveal prominent differences in these observables between the two systems, particularly in the most central collisions. Comparisons with hydrodynamic model calculations indicate a large quadrupole and octupole deformation in the ground states of $^{238}$U nuclei, consistent with low-energy experiments. However, data also imply a small deviation from axial symmetry [1,2,3]. We also present the first measurements of $v_n$ in $^{16}$O+$^{16}$O collisions [4,5], providing insight into the impact of nucleon-nucleon correlations and further shedding light on the initial conditions of QGP droplets.
[1] STAR Collaboration, Nature 635, 67-72 (2024)
[2] STAR Collaboration, arXiv:2506.17785, Under ROPP review
[3] C. Zhang, J. Jia, J. Chen, C. Shen, L. Liu, arXiv:2504.15245
[4] STAR Collaboration, In preparation
[5] C. Zhang, J. Chen, G. Giacalone, S. Huang, J. Jia, Y.-G. Ma, PLB862, 139322(2025)
