重离子碰撞中横向球度与椭圆流的内在耦合
Intrinsic coupling between transverse spherocity and elliptic flow in heavy-ion collisions
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中文总结 AI 辅助
研究重离子碰撞中横向球度与椭圆流的关系，通过多种模拟和计算表明二者存在内在耦合，横向球度与椭圆流系数$v_{2}$有反相关，应将横向球度视为集体动量空间各向异性的探针，为相关物理结论提供新视角。
中文摘要 AI 辅助
横向球度（$S_{0}$）是一种广泛用于根据碰撞事件拓扑结构对其进行分类的事件形状可观测量，特别是区分喷注状事件和各向同性事件。低球度事件通常被解释为与增强的喷注活动有关。本文通过玩具蒙特卡罗模拟、多相输运（AMPT）模型计算以及球度可观测量的解析公式，表明横向球度与椭圆流系数$v_{2}$存在内在关联。这种关联源于使球度最小化的轴与事件对称平面重合，导致即使在没有真正喷注状拓扑结构的情况下，具有较大椭圆各向异性的事件自然呈现较小的球度值。进一步表明这种内在关系导致横向球度与$v_{2}$之间存在固有反相关，意味着重离子碰撞中先前归因于低球度事件增强的喷注状性质的几个特征，可理解为集体各向异性流的结果。结果表明，在重离子碰撞中，横向球度应主要解释为集体动量空间各向异性的探针，而非喷注状事件拓扑结构的直接度量。因此，从球度选择事件得出的物理结论应明确考虑其与椭圆流的内在相关性。
英文摘要
Transverse spherocity ($S_{0}$) is an event-shape observable widely used to classify collision events according to their topology, particularly to distinguish jet-like from isotropic events. Low-spherocity events are generally interpreted as being associated with enhanced jet activity. This event classification has also been applied to heavy-ion collisions to investigate the influence of event topology on several observables, including elliptic flow and constituent-quark-number scaling. In this work, we demonstrate that such an interpretation requires careful reconsideration. Using toy Monte Carlo simulations, A Multiphase Transport (AMPT) model calculations, and an analytical formulation of the spherocity observable, we show that transverse spherocity is intrinsically related to the elliptic flow coefficient, $v_{2}$. This connection arises because the axis that minimizes the spherocity aligns with the event symmetry plane, causing events with larger elliptic anisotropy to naturally exhibit smaller spherocity values even in the absence of genuine jet-like topologies. We further show that this intrinsic relation gives rise to an inherent anti-correlation between transverse spherocity and $v_{2}$, implying that several characteristics previously attributed to the enhanced jet-like nature of low-spherocity events in heavy-ion collisions can instead be understood as consequences of collective anisotropic flow. Our results indicate that, in heavy-ion collisions, transverse spherocity should be interpreted primarily as a probe of the collective momentum-space anisotropy rather than as a direct measure of jetty event topology. Consequently, physics conclusions drawn from spherocity-selected events should explicitly account for its intrinsic correlation with elliptic flow.
