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arXiv · 2109.09956

Lambda polarization in $^{108}$Ag +$^{108}$Ag and $^{197}$Au +$^{197}$Au collisions around a few GeV

Xian-Gai Deng·Xu-Guang Huang·Yu-Gang Ma
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Abstract

Within the framework of Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model, we extract the global spin polarization of $Λ$ hyperon in $^{108}$Ag + $^{108}$Ag and $^{197}$Au + $^{197}$Au collisions at $\sqrt{s_{\rm NN}} = 2.42 - 62.4$ GeV. We use two different approaches to calculate the $Λ$ polarization $P_y$: approach I is based on equilibrium assumption so that $P_y$ is determined by thermal vorticity and approach II assumes a proportional relation between $P_y$ and the system's angular momentum in $Λ$'s rest frame. We find that both approaches can describe the experimental data at low energies around a few GeV but only approach I describes well also higher-energy data. This suggests that at higher energies the relativistic effect plays an important role. After taking into such effect properly, the relativity-improved approach II can describe the higher-energy data as well.

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Xian-Gai Deng, Xu-Guang Huang, Yu-Gang Ma. 2022-11-15. Lambda polarization in $^{108}$Ag +$^{108}$Ag and $^{197}$Au +$^{197}$Au collisions around a few GeV. https://doi.org/10.1016/j.physletb.2022.137560

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