Event-by-event correlations between Λ (Λ¯) hyperon global polarization and handedness with charged hadron azimuthal separation in Au+Au collisions at sNN=27 GeV from STAR

Résumé fourni par la source

Global polarizations ($P$) of $\mathrm{\ensuremath{\Lambda}} (\overline{\mathrm{\ensuremath{\Lambda}}})$ hyperons have been observed in noncentral heavy-ion collisions. The strong magnetic field primarily created by the spectator protons in such collisions would split the $\mathrm{\ensuremath{\Lambda}}$ and $\overline{\mathrm{\ensuremath{\Lambda}}}$ global polarizations ($\mathrm{\ensuremath{\Delta}}P={P}_{\mathrm{\ensuremath{\Lambda}}}\ensuremath{-}{P}_{\overline{\mathrm{\ensuremath{\Lambda}}}}<0$). Additionally, quantum chromodynamics 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 ($\mathrm{\ensuremath{\Delta}}n=\frac{{N}_{\text{L}}\ensuremath{-}{N}_{\text{R}}}{\ensuremath{\langle}{N}_{\text{L}}+{N}_{\text{R}}\ensuremath{\rangle}}\ensuremath{\ne}0$) between left- and right-handed $\mathrm{\ensuremath{\Lambda}}$ ($\overline{\mathrm{\ensuremath{\Lambda}}}$) 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 ($\mathrm{\ensuremath{\Delta}}\ensuremath{\gamma}$) and parity-odd azimuthal harmonic observable ($\mathrm{\ensuremath{\Delta}}{a}_{1}$). Measurements of $\mathrm{\ensuremath{\Delta}}P, \mathrm{\ensuremath{\Delta}}\ensuremath{\gamma}$, and $\mathrm{\ensuremath{\Delta}}{a}_{1}$ have not led to definitive conclusions concerning the CME or the magnetic field, and $\mathrm{\ensuremath{\Delta}}n$ has not been measured previously. Correlations among these observables may reveal new insights. This paper reports measurements of correlation between $\mathrm{\ensuremath{\Delta}}n$ and $\mathrm{\ensuremath{\Delta}}{a}_{1}$, which is sensitive to chirality fluctuations, and correlation between $\mathrm{\ensuremath{\Delta}}P$ and $\mathrm{\ensuremath{\Delta}}\ensuremath{\gamma}$ sensitive to magnetic field in $\mathrm{Au}+\mathrm{Au}$ collisions at 27 GeV. For both measurements, no correlations have been observed beyond statistical fluctuations.

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