再论相对论重离子对撞机等压碰撞中的手征磁效应
Revisit the Chiral Magnetic Effect Expectation in Isobaric Collisions at the Relativistic Heavy Ion Collider
摘要：
在相对论重离子对撞机上进行了$\sqrt{s_{_{NN}}}=200$ GeV的$^{96}_{44}$ Ru+ $^{96}_{44}$ Ru和$^{96}_{40}$ Zr+ $^{96}_{40}$ Zr的等压碰撞，以避开大流量诱导背景，寻找量子色动力学（QCD）拓扑特征所预言的手征磁效应（CME）.考虑到同量异位素碰撞的背景大约是Au+Au碰撞的两倍，（由于较小的多重性）和CME信号大约是一半（由于磁场较弱），我们警告说，在$\sim$ 2 $σ$显著性范围内，如果轴向电荷/熵密度（$n_5/s$）和QCD真空跃迁几率是系统无关的。这一预期一般由异常粘性流体动力学（AVFD）模型验证。虽然我们的估计提供了一个近似的“实验”基线，理论上的不确定性仍然很大。
英文摘要：
Isobaric $^{96}_{44}$Ru+$^{96}_{44}$Ru and $^{96}_{40}$Zr+$^{96}_{40}$Zr collisions at $\sqrt{s_{_{NN}}}=200$ GeV have been conducted at the Relativistic Heavy Ion Collider to circumvent the large flow-induced background in searching for the chiral magnetic effect (CME), predicted by the topological feature of quantum chromodynamics (QCD). Considering that the background in isobar collisions is approximately twice that in Au+Au collisions (due to the smaller multiplicity) and the CME signal is approximately half (due to the weaker magnetic field), we caution that the CME may not be detectable with the collected isobar data statistics, within $\sim$2$σ$ significance, if the axial charge per entropy density ($n_5/s$) and the QCD vacuum transition probability are system independent. This expectation is generally verified by the Anomalous-Viscous Fluid Dynamics (AVFD) model. While our estimate provides an approximate "experimental" baseline, theoretical uncertainties on the CME remain large.
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