Freeze-out in narrow and wide layers

The freeze-out of particles from a layer of finite thickness is discussed in a phenomenological kinetic model. The proposed model, based on the Modified Boltzman Transport Equation, is Lorentz invariant and can be applied equally well for the freeze-out layers with space-like and time-like normal vectors. It leads to non-equilibrated post freeze-out distributions. The dependence of the resulting distribution on the thickness of the layer is presented and discussed for a space-like freeze-out scenario.