Probing $\alpha$ clustering in $^{12}\mathrm{C}$ at CSR energies using the Jet AA Microscopic Transport Model

TL;DR

This study explores how alpha clustering in carbon-12 influences initial geometry and final-state observables in low-energy nuclear collisions, revealing that certain radial and flow measurements can serve as probes for nuclear structure effects.

Contribution

It demonstrates the sensitivity of radial observables and flow harmonic correlations to alpha clustering in $^{12}C$ using the JAM model at CSR energies.

Findings

Alpha clustering results in a more compact participant configuration.

Radial observables like mean transverse momentum are sensitive to clustering.

Flow harmonic magnitudes are enhanced for alpha-clustered configurations.

Abstract

We investigate the sensitivity of low-energy nuclear collisions to intrinsic nuclear structure by studying the interplay between initial-state geometry and final-state observables in C+C and C+Pb collisions at $\sqrt{s_{NN}}=2.36$~GeV, relevant for experiments at the Cooling Storage Ring (CSR) facility in Lanzhou and forthcoming experiments at the High Intensity heavy-ion Accelerator Facility (HIAF) in Huizhou. Calculations are performed within the Jet AA Microscopic Transport Model (JAM) using Woods--Saxon and triangular $\alpha$-clustered configurations for the $^{12}C$ nucleus. The initial geometry is characterized in terms of transverse size, compactness, eccentricities, and their ensemble-averaged fluctuations. We find that $\alpha$ clustering leads to a more compact participant configuration than the Woods--Saxon case, while transverse-size and eccentricity fluctuations show only weak sensitivity to clustering. At this beam energy, radial observables remain sensitive to geometric compactness, with the ensemble-averaged proton mean transverse momentum $\langle p_T \rangle$ enhanced for $\alpha$-clustered configurations, whereas pions show little sensitivity. The anisotropic response is examined using flow harmonic coefficients. We find an enhancement of the root-mean-square flow magnitudes, $v_n\{2\} = \sqrt{\langle v_n^2\rangle}$, for $\alpha$-clustered configurations at large $N_{part}$, while the ensemble-averaged fluctuation strength of individual harmonics remains small. Symmetric cumulants of the initial-state eccentricities show sensitivity to clustering, whereas the corresponding ensemble-averaged correlations among final-state flow harmonics do not exhibit a comparably strong separation. These results indicate that radial observables and correlation-based flow measurements provide complementary probes of $\alpha$ clustering in low-energy nuclear collisions.