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The longitudinal structure of the quark-gluon plasma (QGP) consists of several components spanning various scales. However, its short-range features are often obscured by final-state non-flow correlations. Here, we introduce a data-driven approach to separate initial state structures from non-flow effects. The longitudinal structure is found having two distinct components: one that reflects the global twisted geometry of the QGP, and another that captures localized fluctuations in rapidity. The characteristics of this second component, contributing to short- and medium-range flow decorrelations, can be quantified by comparing collisions of nuclei with different shapes. This study represents the first successful attempt to disentangle long- and short-range flow decorrelations from non-flow backgrounds, providing new insights into the initial conditions of heavy-ion collisions., Comment: 6 pages, 4 figures

The study of quark-gluon plasma (QGP) is hindered by our limited understanding of its initial conditions, particularly its longitudinal structure. We propose a novel approach that entails analyzing collisions involving nuclei of similar masses but different deformations. This strategy allows us to vary the initial conditions and collective expansion of the QGP, while minimizing the influence of non-flow correlations. Using a dynamical transport model, we have for the first time extracted the complete longitudinal structure of elliptic flow ($v_2$). Our findings reveal that although deformation significantly enhances the overall magnitude of $v_2$, it does not alter its longitudinal profile. This approach not only enables the separation of the rapidity dependence of flow from its rapidity decorrelations but also prompts further investigation into other nuclear structural features, such as nuclear skin thickness, to advance our understanding of the QGP's initial conditions., Comment: 6 pages, 6 figures

Investigating nucleon-nucleon correlations inherent to the strong nuclear force is one of the core goals in nuclear physics research. We showcase the unique opportunities offered by collisions of $^{16}$O nuclei at high-energy facilities to reveal detailed many-body properties of the nuclear ground state. We interface existing knowledge about the geometry of $^{16}$O coming from \textit{ab-initio} calculations of nuclear structure with transport simulations of high-energy $^{16}$O+$^{16}$O collisions. Bulk observables in these processes, such as the elliptic flow or the fluctuations of the mean transverse momentum, are found to depend significantly on the input nuclear model and to be sensitive to realistic clustering and short-range repulsive correlations, effectively opening a new avenue to probe these features experimentally. This finding demonstrates collisions of oxygen nuclei as a tool to elucidate initial conditions of small collision systems while fostering connections with effective field theories of nuclei rooted in quantum chromodynamics (QCD).

In this proceeding, we present the first measurements of azimuthal anisotropies, $v_2$ and $v_3$, in $^{16}$O+$^{16}$O collisions at 200 GeV as a function of transverse momentum and multiplicity, by using two- and four-particle correlation methods. We compare our measurements with STAR measurements of $v_n$ in \dau and \heau collisions to provide insight into the impact of system symmetry on initial condition for small systems. We also investigate the ratio $v_2\{4\}/v_2\{2\}$ as a function of centrality, which is expected to be sensitive to nucleon-nucleon correlation in the $^{16}$O nucleus., Comment: 4 Pages, 3 figures, Quark Matter 2023 Proceeding

A major goal of the hot QCD program, the extraction of the properties of the quark gluon plasma (QGP), is currently limited by our poor knowledge of the initial condition of the QGP, in particular how it is shaped from the colliding nuclei. To attack this limitation, we propose to exploit collisions of selected species to precisely assess how the initial condition changes under variations of the structure of the colliding ions. This knowledge, combined with event-by-event measures of particle correlations in the final state of heavy-ion collisions, will provide in turn a new way to probe the collective structure of nuclei, and to confront and exploit the predictions of state-of-the-art ab initio nuclear structure theories. The US nuclear community should capitalize on this interdisciplinary connection by pursuing collisions of well-motivated species at high-energy colliders., Comment: 23 pages, 6 figures

To assess the properties of the quark-gluon plasma formed in nuclear collisions, the Pearson correlation coefficient between flow harmonics and mean transverse momentum, $\rho\left(v_{n}^{2},\left[p_{\mathrm{T}}\right]\right)$, reflecting the overlapped geometry of colliding atomic nuclei, is measured. $\rho\left(v_{2}^{2},\left[p_{\mathrm{T}}\right]\right)$ was found to be particularly sensitive to the quadrupole deformation of the nuclei. We study the influence of the nuclear quadrupole deformation on $\rho\left(v_{n}^{2},\left[p_{\mathrm{T}}\right]\right)$ in $\rm{Au+Au}$ and $\rm{U+U}$ collisions at RHIC energy using $\rm{AMPT}$ transport model, and show that the $\rho\left(v_{2}^{2},\left[p_{\mathrm{T}}\right]\right)$ is reduced by the prolate deformation $\beta_2$ and turns to change sign in ultra-central collisions (UCC)., Comment: Proceedings for the 50th International Symposium on Multiparticle Dynamics, Zurich, Europe, 12-16 July 2021

In heavy ion collisions, elliptic flow $v_2$ and radial flow, characterized by event-wise average transverse momentum $[p_{\mathrm{T}}]$, are related to the shape and size of the overlap region, which are sensitive to the shape of colliding atomic nuclei. The Pearson correlation coefficient between $v_2$ and $[p_{\mathrm{T}}]$, $\rho_2$, was found to be particularly sensitive to the quadrupole deformation parameter $\beta$ that is traditionally measured in low energy experiments. Built on earlier insight that the prolate deformation $\beta>0$ reduces the $\rho_2$ in ultra-central collisions (UCC), we show that the prolate deformation $\beta<0$ enhances the value of $\rho_2$. As $\beta>0$ and $\beta<0$ are the two extremes of triaxiality, the strength and sign of $v_2^2-[p_{\mathrm{T}}]$ correlation can be used to provide valuable information on the triaxiality of the nucleus. Our study provide further arguments for using the hydrodynamic flow as a precision tool to directly image the deformation of the atomic nuclei at extremely short time scale ($<10^{-24}$s)., Comment: 13 pages, 10 figures, update to the Accepted version

The observation of multi-particle azimuthal correlations in high-energy small-system collisions has led to intense debate on its origin and the possible coexistence from two competing theoretical scenarios: one based on initial-state intrinsic momentum anisotropy (ISM), and the other based on final-state collective response to the collision geometry (FSM). To complement the previous scan of asymmetric collision systems ($p$+Au, $d$+Au and He+Au), we propose a scan of small symmetric collision systems at RHIC, such as C+C, O+O, Al+Al and Ar+Ar $\sqrt{s_{\mathrm{NN}}}=0.2$ TeV, to provide further insights in disentangling contributions from these two scenarios. These symmetric small systems have the advantage of providing a better controlled initial geometry dominated by the average shape of the overlap region, as opposed to fluctuation-driven geometries in asymmetric systems. A transport model is employed to investigate the expected geometry response in the FSM scenario. Different trends of elliptic flow with increasing charge particle multiplicity are observed between symmetric and asymmetric systems, while triangular flow appears to show a similar behavior. Furthermore, a comparison of O+O collisions at $\sqrt{s_{\mathrm{NN}}}=0.2$ TeV and at $\sqrt{s_{\mathrm{NN}}}=2.76-7$ TeV, as proposed at the LHC, provides a unique opportunity to disentangle the collision geometry effects at nucleon level from those arising from subnucleon fluctuations., Comment: 6 pages, 6 figures