Study the effects of pre-hydrodynamic flow in heavy-ion collisions at the RHIC Beam Energy Scan program

The (3+1)D hydrodynamics + hadronic transport hybrid models are effective quantitative tools to study the dynamics of relativistic heavy-ion collisions and to extract the transport properties of the Quark-Gluon Plasma. For collisions with $sqrt{s_mathrm{NN}} sim O(10)$~GeV, the pre-equilibrium evolution before hydrodynamics plays an important role because it can reach up to 30\% of the total collision lifetime. In this work, we parameterize the transverse pre-hydrodynamic flow with a blast-wave-like profile, $v_perp(r_perp) = tanh(alpha r_perp)$, for individual hot spots. We will show that the flow profiles with certain values of $alpha$ can reproduce those generated from the free-streaming model. We further perform a systematic study on how the pre-hydrodynamic flow affects final-state observables in heavy-ion collisions at the RHIC Beam Energy Scan program. We will show its sensitivity to the anisotropic flow ratio $v_3/v_2$ and the HBT radii.