Local spin polarization by color-field correlators and momentum anisotropy

Abstract

We study the local spin polarization of quarks induced by color-field correlators stemming from the correlation of chromo-Lorentz force and chromo-magnetic polarization or chromo-spin Hall effect in the presence of momentum anisotropy. Such effects can trigger longitudinal polarization from fluctuating color fields in glasma or quark gluon plasma phases with transverse expansion for relativistic heavy ion collisions. Especially, from the glasma effect, the resulting longitudinal polarization spectrum of $Λ/\barΛ$ hyperons has a sinusoidal structure with twice the azimuthal angle relative to the anisotropic direction. An order-of-magnitude estimate of the effect aligns with experimental observations. Our findings highlight the significant role of coherent gluon fields as a novel source for spin polarization phenomena in high-energy nuclear collisions.

Figures (4)

• Figure 1: A schematic figure for the transverse plane of the QCD medium (glasma or QGP), where the region inside the dashed ellipse represents the core, while the region between the solid ellipse and the dashed one corresponds to the corona. Also, $\bm u$ and $\bm p$ denote the flow velocity and momentum of the quark on the medium surface.
• Figure 2: $\mathcal{P}^z$ at $y_p=0$ from glasma and Eq. (\ref{['eq:quark_Sch_dis']}) for quark distributions. The upper panel shows $\phi$ dependence with $p_{T}=2$ GeV and the lower shows $p_{T}$ dependence with $\phi=\pi/4$. The blue dashed and red solid curves correspond to $Q_s=1.5$ GeV and $Q_s=2$ GeV, respectively.
• Figure 3: $\mathcal{P}^z$ at $y_p=0$ from glasma and Eq. (\ref{['eq:quark_dis']}) for quark distributions. The same color assignment as Fig. \ref{['fig:GL_Sch_Pz']} for $c=1$. The additional red dotted curves represent the cases with $Q_s=2$ GeV and $c=0.5$ for comparisons.
• Figure 4: $\mathcal{P}^z$ at $y_p=0$ from QGP. The upper panel shows $\phi$ dependence with $p_{T}=2$ GeV and the lower shows $p_{T}$ dependence with $\phi=\pi/4$. The blue dashed and red solid curves correspond to $0-15$% centrality and $30-60$% centrality, respectively.