Speaker
Description
Collectivity in small systems is a crucial area of study in high-energy nuclear physics, as it provides valuable insights into initial conditions and pre-equilibrium stages in heavy-ion collisions. The small system collision scan at RHIC, including both symmetric and asymmetric small systems (O+O $>$ $^{3}$He$+$Au $>$ $d$$+$Au $>$ $p$$+$Au $>$ $\gamma+$Au), provides a better understanding of how collectivity emerges and evolves with system size.
We analyze a large sample of minimum bias and central triggered $^{16}$O+$^{16}$O collisions at $\sqrt{s_{NN}}$ = 200 GeV and inclusive $\gamma$+Au processes (center-of-mass energy around 40 GeV) by triggering ultra-peripheral events in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Using two- and four-particle correlation methods, we present the first measurements of azimuthal anisotropies, $v_2$ and $v_3$, in $^{16}$O+$^{16}$O and $\gamma$+Au collisions as a function of $p_{\mathrm{T}}$ and multiplicity. We compare our measurements with STAR measurements of $v_n$ in $p/d/^3$He+Au collisions and hydrodynamic model calculations.
New $v_{n}$ measurements in $^{16}$O+$^{16}$O collisions provide insight into the impact of system symmetry on initial condition and pre-equilibrium dynamics, compared to the previously studied asymmetric systems $p/d/^3$He+Au. We also investigate the ratio $v_2\{4\}/v_2\{2\}$ and correlations between $v_n$ and mean $p_{\mathrm{T}}$ as a function of multiplicity, which are sensitive to initial momentum anisotropy, subnucleon fluctuations, and clustering in the $^{16}$O nucleus. In addition, $v_{n}$ measurements in $\gamma$+Au processes play an important role in understanding the origin of collectivity and lay the foundation for searching for many-body systems exhibiting collective behavior in photon-induced processes at the EIC.
| Category | Experiment |
|---|---|
| Collaboration (if applicable) | STAR Collaboration |
