论文标题
搜索$ \ sqrt {s _ {_ {_ {\ rm {nn}}}}} = 27 $ GEV的au+au碰撞中的手性磁效果
Search for the Chiral Magnetic Effect in Au+Au collisions at $\sqrt{s_{_{\rm{NN}}}}=27$ GeV with the STAR forward Event Plane Detectors
论文作者
论文摘要
手性磁效应(CME)的决定性实验测试被认为是相对论重型离子对撞机(RHIC)的主要科学目标之一,用于理解量子染色体动力学的非平凡拓扑波动。在重离子碰撞中,预计CME会导致整个反应平面的电荷分离现象,其强度可能非常依赖能量。先前的CME搜索集中在顶级RHIC能源碰撞上。在这封信中,我们在$ \ sqrt {s _ {_ {\ rm {nn}}}}} = 27 $ gev中提供了低能搜索au+au碰撞中的CME。我们测量椭圆流缩放电荷依赖性相关器相对于事件平面,这些事件平面在中高度$ |η| <1.0 $和正向快速性$ 2.1 <|η| <5.1 $。我们根据中央和正向速度的椭圆流平面($ψ_2$)的定向流平面($ψ_1$)比较结果。预计CME方案将导致相对于$ψ_1$的相关性较大,而不是$ψ_2$,而流动驱动的背景方案将导致两个事件平面的一致结果。在10-50 \%的中心性中,发现使用三个不同事件平面的结果在实验不确定性中是一致的,这表明流动驱动的背景场景主导了测量。我们在95 \%置信度下从流动驱动的背景方案中获得了上限。这项工作通过RHIC Beam Energy Scan阶段II的高统计数据打开了可能的路线图,以实现未来的CME搜索。
A decisive experimental test of the Chiral Magnetic Effect (CME) is considered one of the major scientific goals at the Relativistic Heavy-Ion Collider (RHIC) towards understanding the nontrivial topological fluctuations of the Quantum Chromodynamics vacuum. In heavy-ion collisions, the CME is expected to result in a charge separation phenomenon across the reaction plane, whose strength could be strongly energy dependent. The previous CME searches have been focused on top RHIC energy collisions. In this Letter, we present a low energy search for the CME in Au+Au collisions at $\sqrt{s_{_{\rm{NN}}}}=27$ GeV. We measure elliptic flow scaled charge-dependent correlators relative to the event planes that are defined at both mid-rapidity $|η|<1.0$ and at forward rapidity $2.1 < |η|<5.1$. We compare the results based on the directed flow plane ($Ψ_1$) at forward rapidity and the elliptic flow plane ($Ψ_2$) at both central and forward rapidity. The CME scenario is expected to result in a larger correlation relative to $Ψ_1$ than to $Ψ_2$, while a flow driven background scenario would lead to a consistent result for both event planes. In 10-50\% centrality, results using three different event planes are found to be consistent within experimental uncertainties, suggesting a flow driven background scenario dominating the measurement. We obtain an upper limit on the deviation from a flow driven background scenario at the 95\% confidence level. This work opens up a possible road map towards future CME search with the high statistics data from the RHIC Beam Energy Scan Phase-II.