Collective flow and fluid behavior in p/d/3He+Au collisions at GeV* * Supported in part by the National Natural Science Foundation of China (12247107, 12075007, 12147173 (Baochi Fu))

By varying the intrinsic initial geometry, p/d/³He+Au collisions at the Relativistic Heavy Ion Collider (RHIC) provide a unique opportunity to understand the collective behavior and probe possible sub-nucleon fluctuations in small systems. In this study, we employed the hybrid model under TRENTo initial conditions to study the collective flow and fluid behavior in p/d/³He+Au collisions. With fine-tuned parameters, can describe the and data from the PHENIX and STAR collaborations. However, for certain parameter sets with initial sub-nucleon fluctuations, the hydrodynamic simulations already go beyond their limits with an average Knudsen number clearly larger than unity. Our calculations demonstrate that, for a meaningful evaluation of the fluid behavior in small systems, model simulations must also pay attention to the validity range of hydrodynamics.