The event-plane method, which is widely used to analyze anisotropic flow in nucleus-nucleus collisions, is known to be biased by nonflow effects,especially at high $p_t$. Various methods (cumulants, Lee-Yang zeroes) have been proposed to eliminate nonflow effects, but their implementation is tedious, which has limited their application so far. In this paper, we show that the Lee-Yang-zeroes method can be recast in a form similar to the standard event-plane analysis. Nonflow correlations are strongly suppressed by using the information from the length of the flow vector, in addition to the event-plane angle. This opens the way to improved analyses of elliptic flow and azimuthally-sensitive observables at RHIC and LHC.
We present the first calculation of longitudinal decorrelation of anisotropic flow at RHIC Beam Energy Scan (BES) energies using event-by-event viscous hydrodynamic model (vHLLE), with two different initial states (GLISSANDO2 and UrQMD) and hadronic cascade. We investigate the origin of the observed decorrelation by checking separately flow angle and flow magnitude decorrelation and by calculating decorrelation in the initial state eccentricity.
Decorrelation of the elliptic flow in rapidity is calculated within a hybrid approach which includes event-by-event viscous fluid dynamics and final state hadronic cascade model. The simulations are performed for Au+Au collisions at center-of-mass collision energies of 27 and 200 GeV per nucleon pair, as well as various colliding systems at 72 GeV per nucleon pair. Initial conditions determined by an extended Monte Carlo Glauber model show better agreement with experimental data than initial conditions from the UrQMD transport model. We show how the observed decorrelation is connected with the…
Effects of initial flow velocity fluctuation in event-by-event (3+1)D hydrodynamics
在（3+1）D理想流体力学模型中，采用AMPT Monte Carlo模型给出的涨落初始条件，研究了高能重离子碰撞中的强子谱和椭圆流.在RHIC和LHC的能量从事件的模拟结果与实验数据进行了比较。初始能量密度的涨落不仅来自于重叠核子的相干软相互作用的数目，而且还来自于每次二元核子碰撞中的非相干半硬部分子散射。半硬部分子散射的微喷流被假定为局部热化通过高斯涂抹，并引起非零的初始局部流速。由于初始径向流速的非零性，初始流速的涨落导致末态强子的横动量谱更硬。在快度分布的初始波动导致扩大热点在纵向方向上，并示出在大的横向动量，导致一个相当大的减少最终强子椭圆流。
A method for studying initial geometry fluctuations via event plane correlations in heavy ion collisions
提出了一种利用傅里叶分析技术测量重离子碰撞中两个或多个不同阶数事件面的相对方位角分布的方法。分析过程表明，涉及两个和三个事件平面（Phi_n，Phi_m和Phi_h）的相关性。这些分布的傅里叶系数与前人提出的余弦（6Phi_2-6Phi_3）和余弦（Phi_1+2Phi_2-3Phi_3）等修正因子相一致，因此该方法为同时研究这些修正因子提供了一个自然的框架。使用Monte Carlo Glauber模型来模拟Au+Au碰撞与波动的初始几何形状，我们能够确定几个新的两个或三个平面具有相当大的幅度，应该通过实验测量的碰撞。
