Probing $\alpha$ clustering in ${}^{12}\mathrm{C}$ at energies available at the Cooling Storage Ring facility using the Jet AA Microscopic Transport Model

Abstract

I investigate the sensitivity of low-energy nuclear collisions to intrinsic nuclear structure through the interplay between initial-state geometry and final-state observables in C+C and C+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.36$~GeV, relevant to experiments at the Cooling Storage Ring (CSR) in Lanzhou and the forthcoming High Intensity heavy-ion Accelerator Facility (HIAF) in Huizhou. Calculations are performed using the Jet AA Microscopic Transport Model (JAM), with Woods--Saxon and triangular $\alpha$-clustered configurations of the ${}^{12}\mathrm{C}$ nucleus. The initial geometry is characterized by transverse size, compactness, eccentricities, and their fluctuations. The $\alpha$-clustered configuration produces a more compact participant system, while transverse-size and eccentricity fluctuations are only weakly affected. Radial observables remain sensitive to this compactness: the ensemble-averaged proton mean transverse momentum $⟨p_T⟩$ is enhanced for the clustered configuration, whereas pion observables show little sensitivity. In contrast, flow harmonics and their event-by-event fluctuations show no appreciable dependence on clustering. Normalized symmetric cumulants of initial-state eccentricities are sensitive to clustering, but the corresponding final-state flow cumulants show no comparably strong separation. These results suggest that dynamical evolution at this energy substantially weakens the imprint of initial $\alpha$ clustering on anisotropic-flow observables, while radial observables remain promising probes of nuclear structure.

arXiv comment13 pages, 21 figures, accepted for publication in PRC