Event-by-event correlations between $\Lambda$ ($\bar{\Lambda }$) 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 $\Lambda$ ($\bar{\Lambda }$) 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 $\Lambda$ and $\bar{\Lambda }$ global polarizations ($\Delta P=P_{\Lambda }-P_{\bar{\Lambda }}<0$). 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 ($\Delta n=\frac{N_{\text{L}}-N_{\text{R}}}{⟨N_{\text{L}}+N_{\text{R}}⟩}\ne 0$) between left- and right-handed $\Lambda$ ($\bar{\Lambda }$) 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 ($\Delta \gamma$) and parity-odd azimuthal harmonic observable ($\Delta a_1$). Measurements of $\Delta P$, $\Delta \gamma$, and $\Delta a_1$ have not led to definitive conclusions concerning the CME or the magnetic field, and $\Delta n$ has not been measured previously. Correlations among these observables may reveal new insights. This paper reports measurements of correlation between $\Delta n$ and $\Delta a_1$, which is sensitive to chirality fluctuations, and correlation between $\Delta P$ and $\Delta \gamma$ sensitive to magnetic field in Au+Au collisions at 27 GeV. For both measurements, no correlations have been observed beyond statistical fluctuations.

arXiv comment10 pages, 10 figures; paper from the STAR Collaboration

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