Event-by-event correlations between $\hat{I}›$ ($\bar{\hat{I}}›$) hyperon global polarization and handedness with charged hadron azimuthal separation in Au+Au collisions at $\sqrt{s_{\text{NN}}}=27\text{ GeV}$ from STAR

Abstract

Global polarizations ($P$) of $\hat{I}›$ ($\bar{\hat{I}}›$) hyperons have been observed in non-central heavy-ion collisions. The strong magnetic field primarily created by the spectator protons in such collisions would split the $\hat{I}›$ and $\bar{\hat{I}}›$ global polarizations ($\hat{I}”P=P_{\hat{I}}›-P_{\bar{\hat{I}}›}<0$). Additionally, quantum chromodynamics (QCD) predicts topological charge fluctuations in vacuum, resulting in a chirality imbalance or parity violation in a local domain. This would give rise to an imbalance ($\hat{I}”n=\frac{N_{\text{L}}-N_{\text{R}}}{⟨N_{\text{L}}+N_{\text{R}}⟩}\ne 0$) between left- and right-handed $\hat{I}›$ ($\bar{\hat{I}}›$) as well as a charge separation along the magnetic field, referred to as the chiral magnetic effect (CME). This charge separation can be characterized by the parity-even azimuthal correlator ($\hat{I}”{\hat{I}}^3$) and parity-odd azimuthal harmonic observable ($\hat{I}”a_1$). Measurements of $\hat{I}”P$, $\hat{I}”{\hat{I}}^3$, and $\hat{I}”a_1$ have not led to definitive conclusions concerning the CME or the magnetic field, and $\hat{I}”n$ has not been measured previously. Correlations among these observables may reveal new insights. This paper reports measurements of correlation between $\hat{I}”n$ and $\hat{I}”a_1$, which is sensitive to chirality fluctuations, and correlation between $\hat{I}”P$ and $\hat{I}”{\hat{I}}^3$ sensitive to magnetic field in Au+Au collisions at 27 GeV. For both measurements, no correlations have been observed beyond statistical fluctuations.

10 pages, 10 figures; paper from the STAR Collaboration