论文标题
搜索u+u和au+au碰撞中的CME，并以不同的处理背景的方法搜索
Search for CME in U+U and Au+Au collisions in STAR with different approaches of handling backgrounds
论文作者
论文摘要
手性磁效应（CME）是指沿着左手和右夸克之间强的磁场的电荷分离，这是由与QCD真空波动的拓扑Gluon场相互作用引起的。我们提出了两种处理三粒子相关器（$δγ_{112} $）的主要椭圆流（$ v_2 $）背景的方法，对CME敏感。在第一种方法中，我们介绍$δγ_{112} $和$Δγ_{123} $测量在U+U和Au+Au碰撞中。 While hydrodynamic simulations including resonance decays and local charge conservation predict that $Δγ_{112}$ scaled by $N_{\rm part}/v_2$ will be similar in U+U and Au+Au collisions, the projected B-field exhibits a distinct difference between the two systems and with varying $N_{\rm part}$.因此，U+U和AU+AU碰撞提供对CME信号和背景的期望不同的配置。此外，由$ n _ {\ rm part}/v_3 $缩放的三粒子可观察的$Δγ_{123} $仅针对背景提供基线测量。在第二种方法中，我们通过测量$Δγ_{112} $来处理$ v_2 $的背景，相对于通过零度量量热比特和按时间投影室测量的参与者测量的观众平面。这些测量值包含来自CME信号的不同贡献（由于观众而沿B场）和$ v_2 $背景（由参与者几何确定）。使用两个$δγ_{112} $测量值，可以确定可能的CME信号和背景贡献。我们在$ \ sqrt {s_ {nn}} = $ 27 GEV的Au+Au碰撞中报告了这样的测量，并与新安装的事件平面检测器一起报告，并报告U+U系统中的新发现，其中预计观众聚合平面相关性与AU+AU碰撞中的这些相关性有所不同。
The chiral magnetic effect (CME) refers to charge separation along a strong magnetic field between left- and right-handed quarks, caused by interactions with topological gluon fields from QCD vacuum fluctuations. We present two approaches to handle the dominant elliptic flow ($v_2$) background in the three-particle correlator ($Δγ_{112}$), sensitive to CME. In the first approach, we present the $Δγ_{112}$ and $Δγ_{123}$ measurements in U+U and Au+Au collisions. While hydrodynamic simulations including resonance decays and local charge conservation predict that $Δγ_{112}$ scaled by $N_{\rm part}/v_2$ will be similar in U+U and Au+Au collisions, the projected B-field exhibits a distinct difference between the two systems and with varying $N_{\rm part}$. Therefore, U+U and Au+Au collisions provide configurations with different expectations for both CME signal and background. Moreover, the three-particle observable $Δγ_{123}$ scaled by $N_{\rm part}/v_3$ provide baseline measurement for only the background. In the second approach, we handle the $v_2$ background by measuring $Δγ_{112}$ with respect to the planes of spectators measured by Zero Degree Calorimeters and participants measured by Time Projection Chamber. These measurements contain different amounts of contributions from CME signal (along B-field, due to spectators) and $v_2$ background (determined by the participant geometry). With the two $Δγ_{112}$ measurements, the possible CME signal and the background contribution can be determined. We report such a measurement in Au+Au collisions at $\sqrt{s_{NN}}=$ 27 GeV with the newly installed event plane detector, and report the new findings in U+U system where the spectator-participant plane correlations are expected to differ from those in Au+Au collisions.
