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arXiv 1504.02741hep-ph
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62和200次GeV Au-Au碰撞中无喷流方位四极子的横向快度$\bf y_t$依赖性

Transverse-rapidity $\bf y_t$ dependence of the nonjet azimuth quadrupole from 62 and 200 GeV Au-Au collisions

David T. Kettler, Duncan J. Prindle, Thomas A. Trainor

摘要:

以前测量的四极分量的方位角相关表示的符号$v_2$已被解释为代表椭圆流,流体动力学现象,证明在非中心核-核碰撞中发挥重要作用。$v_2$测量为相对论重离子对撞机(RHIC)的重离子碰撞中形成"完美液体“的结论提供了主要支持。然而,传统的$v_2$方法的基础上一维(1D)方位角相关给出不一致的结果,并可能包括喷流的贡献。在某些情况下,数据趋势似乎与水动力学解释不一致。在这项研究中,我们区分几个组件的二维角相关和隔离的非喷流(新泽西州)的方位角四极表示为$v_2\{\text{2D}\}$。建立了NJ四极子在$y_t$、中心性和碰撞能上的系统变化。我们采用横向快度$y_t$作为速度测量和横向动量$p_t$的对数替代。基于NJ四极趋势,我们得到了一个完全因式分解的通用参数化的数量$v_2\{\text{2D}\}(y_t,b,\sqrt{s_{NN}})$,它描述了中心性,$y_t$和能量依赖。从$y_t$ -差分$v_2(y_t)$数据中,我们分离出四极谱,并推断出具有意外性质的四极源增强。通过2D模型拟合获得的NJ四极$v_2$趋势非常简单。的中心性趋势似乎是不相关的急剧过渡,在射流相关的结构,可能表明快速变化的Au-Au介质的属性。缺乏对应性表明,新泽西州的四极可能是不敏感的,这样的介质。几个四极趋势对水文解释有着有趣的影响。

英文摘要:

Previous measurements of a quadrupole component of azimuth correlations denoted by symbol $v_2$ have been interpreted to represent elliptic flow, a hydrodynamic phenomenon conjectured to play a major role in noncentral nucleus-nucleus collisions. $v_2$ measurements provide the main support for conclusions that a ``perfect liquid'' is formed in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC). However, conventional $v_2$ methods based on one-dimensional (1D) azimuth correlations give inconsistent results and may include a jet contribution. In some cases the data trends appear to be inconsistent with hydrodynamic interpretations. In this study we distinguish several components of 2D angular correlations and isolate a nonjet (NJ) azimuth quadrupole denoted by $v_2\{\text{2D}\}$. We establish systematic variations of the NJ quadrupole on $y_t$, centrality and collision energy. We adopt transverse rapidity $y_t$ as both a velocity measure and as a logarithmic alternative to transverse momentum $p_t$. Based on NJ quadrupole trends we derive a completely factorized universal parametrization of quantity $v_2\{\text{2D}\}(y_t,b,\sqrt{s_{NN}})$ which describes the centrality, $y_t$ and energy dependence. From $y_t$-differential $v_2(y_t)$ data we isolate a quadrupole spectrum and infer a quadrupole source boost having unexpected properties. NJ quadrupole $v_2$ trends obtained with 2D model fits are remarkably simple. The centrality trend appear to be uncorrelated with a sharp transition in jet-related structure that may indicate rapid change of Au-Au medium properties. The lack of correspondence suggests that the NJ quadrupole may be insensitive to such a medium. Several quadrupole trends have interesting implications for hydro interpretations.

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