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arXiv 1709.04723nucl-exhep-ex
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用事例形状工程约束$\sqrt{s_{\rm NN}}$ = 2.76$ TeV Pb-Pb碰撞中手征磁效应的大小

Constraining the magnitude of the Chiral Magnetic Effect with Event Shape Engineering in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76$ TeV

ALICE Collaboration

摘要:

在超相对论重离子碰撞中,椭圆流$v_2$随事件的变化反映了系统初始状态形状的波动。这允许选择具有相同中心性但不同初始几何形状的事件。这种选择技术,事件形状工程,已被用于在$\sqrt{s_{_{\rm NN}}} =2.76$ TeV的铅铅碰撞中的电荷相关的两个和三个粒子的关联分析。两粒子相关器$\langle \cos(φ_α- φ_β) \rangle$,计算电荷$α$和$β$的不同组合,几乎是独立的$v_2$(对于一个给定的中心性),而三粒子相关器$\langle \cos(φ_α+ φ_β- 2Ψ_2) \rangle$的比例几乎线性事件$v_2$和带电粒子赝快度密度。三粒子相关器的电荷依赖性通常被解释为手征磁效应(CME)的证据,手征磁效应是强相互作用的宇称破坏效应。然而,它的测量依赖于$v_2$指向一个大的非CME相关器的贡献。将计算结果与蒙特卡罗计算结果进行比较,发现在95%置信水平下,CME信号对三粒子相关器在10-50%中心度区间内贡献的上限为26-33%。

英文摘要:

In ultrarelativistic heavy-ion collisions, the event-by-event variation of the elliptic flow $v_2$ reflects fluctuations in the shape of the initial state of the system. This allows to select events with the same centrality but different initial geometry. This selection technique, Event Shape Engineering, has been used in the analysis of charge-dependent two- and three-particle correlations in Pb-Pb collisions at $\sqrt{s_{_{\rm NN}}} =2.76$ TeV. The two-particle correlator $\langle \cos(φ_α- φ_β) \rangle$, calculated for different combinations of charges $α$ and $β$, is almost independent of $v_2$ (for a given centrality), while the three-particle correlator $\langle \cos(φ_α+ φ_β- 2Ψ_2) \rangle$ scales almost linearly both with the event $v_2$ and charged-particle pseudorapidity density. The charge dependence of the three-particle correlator is often interpreted as evidence for the Chiral Magnetic Effect (CME), a parity violating effect of the strong interaction. However, its measured dependence on $v_2$ points to a large non-CME contribution to the correlator. Comparing the results with Monte Carlo calculations including a magnetic field due to the spectators, the upper limit of the CME signal contribution to the three-particle correlator in the 10-50% centrality interval is found to be 26-33% at 95% confidence level.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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