重离子碰撞产生的高温高密度物质假设按照统一流体力学模型的规律进行时空演化，并最终经由一固有时为τFO的类空超曲面冻析为带电粒子。统一流体力学模型是一种将Landau与Hwa-Bjorken两著名流体力学模型结合在一起的模型，是一种少有的可精确求解的理论之一。研究表明：BNL-RHIC低能量区重离子碰撞中带电粒子的赝快度分布可由统一流体力学模型很好地描述。这与高能区的情况不同，除了流体外，还需考虑带头粒子的贡献。产生这一差异的原因在于：低能情况下带头粒子的穿透力较弱，带头粒子被流体的贡献所掩盖。
The hot and dense matter created in heavy ion collisions is supposed to have spatiotemporal evolution according to unified hydro model, and finally freeze out into the charged particles via a space-like hypersurface at a proper time τFO. The unified hydro model is a model which integrates Landau and Hwa-Bjorken two famous hydro models together. It is one of few hydro models which can be solved exactly. Shown from the investigations in this paper, the pseudorapidity distribution of charged particles in heavy ion collisions at low BNL-RHIC energies can be well described by the unified hydro model. This is different from that at high energies, where, besides the fluid, the contribution from leading particles should be taken into account. The difference is considered due to the weaker penetration of the leading particles, leading to the leading particles being blanketed by the fluid contribution, at lower collision energies.
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