Elliptic flow orientation, saturation and low $p_t$ behavior

Abstract

We consider general model with factorization between macroscopic flow and matter decay distribution. We show universality of $p_t^2$ behavior of elliptic flow at small $p_t$ for identified final particles in the symmetric nucleus collision. At high $p_t$ we compare non-relativistic and relativistic models for boosted decay distribution. In the relativistic models with distribution having power-like tail we show existence of elliptic flow saturation. This means that the elliptic flow value $v_2$ tend to constant at high $p_t$. We discuss the importance of determination of elliptic flow orientation which can help us to compare different models. For example, we introduce potential expansion model which can reproduce azimuthal asymmetry but based on the assumption that there are only cold strong forces and no thermalization. This model show opposite sign of elliptic flow orientation in comparison with thermal model. We also show that at small $p_t$ sign of elliptic flow can change due to sign of second derivative of decay distribution. This fact tell us that we must more carefully link elliptic flow sign and properties of the model.