An attempt to incorporate separate chemical and thermal freeze outs in hydrodynamics
Abstract
From an analysis of various types of data obtained in relativistic nuclear collisions, the following picture has emerged in thermal and hydrodynamical descriptions: as the fluid expands and cools, particles first undergo a chemical freeze out at Tch.~160-200 MeV then a thermal freeze out at Tth~100-140 MeV. In this paper we show how to incorporate these separate freeze outs consistently in a hydrodynamical code via a modified equation of state (general case) or via a modified Cooper-Frye formula (particular case of Tch. close to Tth. or few particle species undergoing early chemical freeze-out). The modified equation of state causes faster cooling and may have sizable impact on the predicted values of observables.
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