We consider the development of anisotropic flow in an expanding system of particles undergoing very few rescatterings, using a kinetic-theoretical description with a nonlinear collision term. We derive the scaling behaviors of the harmonic coefficients $$v_n$$ <math><msub><mi>v</mi><mi>n</mi></msub></math>  with the initial-state eccentricities and the mean number of rescatterings, and argue that hexagonal flow $$v_6$$ <math><msub><mi>v</mi><mn>6</mn></msub></math>  should follow a nontrivial behavior, different from that of the lower harmonics. Our findings should be observable in experimental data for small systems.

Germany

Nicolas Borghini

Steffen Feld

Nina Kersting

Scaling behavior of anisotropic flow harmonics in the far from equilibrium regime

Dissipative relativistic fluid-dynamical descriptions of the extended fireball formed in high-energy heavy-ion collisions are quite successful; yet they require a prescription for converting the fluid into particles. We present arguments in favour of using a locally anisotropic momentum distribution for the particles emitted from the fluid, so as to smooth out discontinuities introduced by the usual conversion prescriptions. Building on this ansatz, we investigate the effect of the asymmetry on several observables of heavy-ion physics.