arXiv 2012.078982020-12nucl-thhep-ph

横向动量谱的流体速度

Fluid velocity from transverse momentum spectra

Anthony Guillen, Jean-Yves Ollitrault

备注：: Published version; 13 pages, 9 figures
发表信息：: Phys. Rev. C 103, 064911 (2021)
DOI：: 10.1103/PhysRevC.103.064911

摘要：

我们将超相对论核-核碰撞中出射强子的横向动量分布参数化为增强热分布的叠加。在这种方法中，它概括了传统的爆炸波，动量分布是由流体速度的分布。我们分析了这种广义的冲击波参数化和一个完整的水动力计算之间的差异。然后，我们适用于广义爆炸波拟合的实验数据在$\sqrt{s_{\rm NN}}=2.76\ \mathrm{TeV}$铅+铅碰撞。拟合在$p_t\sim 6\ \mathrm{GeV}$以下是合理的，远远超出了通常应用流体力学的范围，但并不完美。基于拟合和数据之间的差异，我们认为，一个理想的流体动力学计算不能同时适合所有确定的粒子光谱，无论具体实施。特别是，数据显示在低$p_t$，其物理解释进行了讨论的π介子显着过剩。数据还表明，随着碰撞变得不那么中心，流体速度的分布变得更宽。这种扩大是由事件的流体动力学计算，在那里它的结果从初始状态波动的中心依赖性解释。

英文摘要：

We parametrize the transverse momentum distribution of outgoing hadrons in ultrarelativistic nucleus-nucleus collisions as a superposition of boosted thermal distributions. In this approach, which generalizes the conventional blast wave, the momentum distribution is determined by the distribution of the fluid velocity. We analyze the difference between this generalized blast-wave parametrization and a full hydrodynamic calculation. We then apply the generalized blast-wave fit to experimental data on Pb+Pb collisions at $\sqrt{s_{\rm NN}}=2.76\ \mathrm{TeV}$. The fit is reasonable up to $p_t\sim 6\ \mathrm{GeV}$, much beyond the range where hydrodynamics is usually applied, but not perfect. Based on the differences between the fit and the data, we argue that an ideal hydrodynamic calculation cannot fit simultaneously all identified particle spectra, irrespective of the specific implementation. In particular, data display a significant excess of pions at low $p_t$, whose physical interpretation is discussed. Data also show that the distribution of the fluid velocity becomes broader as the collision becomes less central. This broadening is explained by event-by-event hydrodynamic calculations, where it results from the centrality dependence of initial-state fluctuations.

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