Speaker
Description
Recently, near-side azimuthal angular correlations across a large pesudorapidity gap, commonly called as long-range ridge-like correlations, have been observed in small collision systems. It opens up opportunities to explore the multiparton dynamics of QCD and the limitation of fluid dynamics description of the matter created in these collisions. We report the STAR measurement of azimuthal harmonics $v_2$ and $v_3$ in the p+Au and d+Au data collected in various energies such as 19.6, 39, 62.4 and 200 GeV. The non-flow contributions, which are suppressed by requiring a large $\Delta\eta$ gap, are estimated in most peripheral collisions and subtracted. After non-flow subtraction at each beam energy, $v_2$ and $v_3$ are obtained as a function of centrality and transverse momentum. The $v_2$ signals are also extracted using four-particle azimuthal correlations, where the influence of non-flow is quantified by comparing to the standard cumulant method, as well as the two-subevent and three-subevent cumulant methods. It is found that both the influence of non-flow and the strength of the long-range $v_2$ and $v_3$ have a strong beam energy dependence. The results are compared to similar studies in peripheral Au+Au collisions and calculations from different models. This measurement provides new constraints on theoretical models of long-range collectivity and its energy dependence in small collision systems.
| Content type | Experiment |
|---|---|
| Collaboration | STAR |
| Centralised submission by Collaboration | Presenter name already specified |
