The nonflow issue in connecting anisotropy measurements to hydrodynamics in relativistic heavy-ion collisions

Understand

Hydrodynamics can describe majority of the measured azimuthal anisotropies in relativistic heavy-ion collisions.

• Many of the anisotropy measurements are contaminated by nonflow correlations (i.e., those unrelated to global event-wise correlations).
• Those nonflow contamination can cause incorrectness or compromise the accuracy of the physics extracted from data-hydrodynamics comparison, particularly when one relies on subtle difference in the measurements.
• In the recent preprint by STAR (arXiv:2401.06625) extracting the Uranium nucleus deformation parameter, nonflow contamination is assessed by subevents in the limited STAR acceptance.