论文标题
使用非流动力学模式研究超遗传对称核碰撞中流体动力行为的发作
Using the non-hydrodynamic mode to study the onset of hydrodynamic behavior in ultraperipheral symmetric nuclear collisions
论文作者
论文摘要
随着将重离子碰撞的流体动力框架扩展到质子 - 普罗顿和其他小能源系统，我们面临着一个问题，即该系统如何获得，并且仍然可以安全地将其作为流体进行安全建模。 $ 2^{nd} $相对论粘性水动力学中所需的运输系数之一是剪切放松时间，其中包括解决Navier-Stokes方程中的因果关系问题。在现象学研究中，该系数被视为一个恒定的，并且在查找和固定剪切粘度与熵密度比的$η/s $方面已经引起了很多关注。该运输系数还恰好控制了非平衡流体动力学理论的非流动力模式。据预测，由于非流动力学模式的优势增加，可观察到的可观察结果对剪切弛豫时间的变化变得敏感，这可能表明流体动力学的崩溃。在这项研究中，我们试图在外围PB-PB碰撞碰撞中测试这一预测，价格为$ 2.76 $ tev和Au-au碰撞，$ 200 $ GEV，ipglasma初始状态和$（2+1） - $尺寸粘性水力动力学。我们发现，椭圆流确实对降低系统尺寸的松弛时间变化表现出足够的敏感性。发现流体动力学的适用性的多重性速度密度限制约为$ dn/dy \ of10 $，并且可能会在该值中进行细化，但对于提高实验数据中的中心性分辨率以在外围碰撞中引用。
With the attempts of extending the hydrodynamic framework of heavy-ion collision to proton-proton and other small and low energy systems, we are confronted with the question of how small the system can get and still be safely modelled as a fluid. One of the transport coefficients required in the $2^{nd}$ order relativistic viscous hydrodynamics is the shear relaxation time, inclusion of which solves the causality violation problem in the Navier-Stokes equation. In phenomenological studies this coefficient has been taken as a constant and much attention has gone into finding and fixing the shear viscosity to entropy density ratio, $η/s$. This transport coefficient also happens to control the non-hydrodynamic mode of the out-of-equilibrium hydrodynamics theory. It has been predicted that for decreasing system size, observables become sensitive to variation in shear relaxation time as a result of increasing dominance of non-hydrodynamic mode, which could potentially indicate breakdown of hydrodynamics. In this study, we try to test this prediction in the peripheral Pb-Pb collisions at $2.76$ TeV and Au-Au collisions at $200$ GeV, with IPGlasma initial condition and $(2+1)-$Dimensional viscous hydrodynamics. We find that elliptic flow does show adequate sensitivity to variation in relaxation time for decreasing system size. The multiplicity rapidity density limit for applicability of hydrodynamics is found to be around $dN/dy\approx10$, with the possibility of refinement in this value given a way to improve the centrality resolution in experimental data for referencing in peripheral collisions.
