Probing the onset of hydrodynamization in peripheral p-Pb collisions at $\sqrt{s_{NN}}=$ 5.02 TeV

Abstract

We estimate the multiplicity scale below which the hydrodynamic description of small systems, such as p-Pb collisions, becomes increasingly sensitive to non-hydrodynamic effects. The sensitivity of experimental observables, namely the elliptic flow coefficient, is investigated by varying the shear relaxation time within second-order relativistic viscous hydrodynamics. To achieve this, a representative system of peripheral p-Pb collisions at $\sqrt{s_{NN}}=$ 5.02 TeV is simulated utilizing the state-of-the-art JETSCAPE event generator. The soft-sector dynamics are modeled via a sequence of initial conditions, a pre-equilibrium stage, hydrodynamics, and a hadronic afterburner. Transverse momentum spectra and rapidity distributions for light-flavored hadrons are extracted and compared with experimental data. The resulting increase in elliptic flow fluctuations indicates a breakdown of fluid behavior at a rapidity density of $dN/dy\sim 10\text{–}15$ for p-Pb collisions at $\sqrt{s_{NN}}=$ 5.02 TeV.