Speaker
Description
Nuclear clustering and intrinsic deformation are important manifestations of many-body correlations in nuclei. At RHIC and the LHC, collective flow and transverse-momentum correlations have been extensively explored as probes of initial-state nuclear structure [1]. Building on recent studies of $\alpha$ clustering and U+U deformation at CSR energies [2,3], we investigate whether transverse-momentum observables provide complementary sensitivity to nuclear structure at the lower collision energies relevant to the CEE experiment at the HIRFL-CSR facility in Lanzhou and the HIAF program in Huizhou. Here, we use the Jet AA Microscopic Transport Model (JAM) at $\sqrt{s_{NN}}=2.36$~GeV. We study $^{12}$C+$^{12}$C, $^{12}$C+$^{208}$Pb, and $^{16}$O+$^{16}$O collisions with different $\alpha$-cluster configurations, and $^{238}$U+$^{238}$U collisions with different quadrupole and hexadecapole deformations. We find that, unlike at high energies, the conventional mapping between initial-state eccentricity and final-state collective flow is substantially weakened at low collision energies, limiting flow as a direct probe of nuclear geometry. In contrast, the mean transverse momentum and its event-by-event cumulants, including $c_2$ and $k_2$, as well as transverse-momentum correlations, remain sensitive to the compactness and underlying configuration of the participant system, carrying quantitative information on clustering and deformation. These results highlight transverse-momentum observables as a complementary approach to probing nuclear many-body structure and motivate their experimental study in the low-energy programs at CEE and HIAF. The fixed-target configurations provide additional flexibility to vary projectile and target nuclei, offering a systematic approach to disentangling different aspects of nuclear structure.
[1]. STAR Collaboration, Nature 635, 67 (2024), J. Jia et al., Nucl. Sci. Tech. 35, 220 (2024).
[2]. S. Singha, arXiv:2602.08288.
[3]. A. Sahoo et al., Phys. Rev. C 109, 054902 (2024).
