Theoretical physics / Elméleti fizika

Exploring the role of initial $\alpha$-clustered nuclear structure on final state flow coefficients via pC, pO and O-O collisions at the LHC

by Aswathy Menon K.R. (IIT Indore, India)

Europe/Budapest
Description

The much-anticipated collisions involving $^{16}\rm O$ nuclei have recently taken place at the Large Hadron Collider (LHC), featuring pO and O-O collisions at $\sqrt{s_{\rm NN}}= 9.62$ TeV and $\sqrt{s_{\rm NN}}= 5.36$ TeV respectively. One of the goals of these collisions is to understand the emergence of hydrodynamic behavior as we move from light to heavy-ion collisions, via the study of anisotropic flow coefficients ($v_{\rm n}$). Another intriguing motivation is to explore the signatures of $\alpha$-clustering in $^{16}\rm O$ nuclei via these relativistic collisions. Since the flow coefficients are sensitive to the initial nuclear structure, our study aims to investigate the influence of the $\alpha$-clustering on the final-state anisotropic flow coefficients \textit{i.e.} elliptic ($v_{2}$) and triangular ($v_{3}$) flow. Firstly, pO and pC collisions are studied at $\sqrt{s_{\rm NN}} = 9.9$~TeV using a multi-phase transport (AMPT) model. Here, $p_{\rm T}$ and $\eta$ spectra, eccentricity ($\langle \epsilon_{2}\rangle$) and triangularity ($\langle \epsilon_{3}\rangle$), $v_{2}$ and $v_{3}$, and their ratios are looked into, for their dependence on collision centrality, collision species and clustered nuclear density profile, in contrast to an unclustered profile. Secondly, we focus on pO collisions at $\sqrt{s_{\rm NN}}= 9.61$ TeV and O-O collisions at $\sqrt{s_{\rm NN}}= 7$ TeV using a hybrid hydrodynamics model viz. IP-Glasma + MUSIC + iSS + UrQMD. Apart from the previously mentioned observables, here, we extend our study to check the dependence of $v_{2}$ and $v_{3}$ on the size of the $\alpha$-cluster ($r_{\alpha}$). We observe a clear dependence of $\alpha$-clustered nuclear profile on all the observables studied, when compared to Woods-Saxon or Sum-of-Gaussians (SOG) density profiles. The trends for $v_{\rm n}$ are significantly influenced by $\alpha$-clustering, where the unique features due to clustering are found to peak near $b/r_{\alpha} = 1$. However, the initial spatial anisotropy is not well carried over to the final state in mid-central/peripheral O-O, pO, and pC collisions due to the less dense system formed in these light-ion collisions.

REFERENCES:
[1] A. Menon Kavumpadikkal Radhakrishnan, S. Prasad, N. Mallick and R. Sahoo, Eur. Phys. J. A 61, 134 (2025).
[2]  A. Menon Kavumpadikkal Radhakrishnan, S. Prasad, N. Mallick, R. Sahoo and G. G. Barnaföldi, [arXiv:2505.22367 [hep-ph]].