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arXiv · 1710.03895

Effects of finite coverage on global polarization observables in heavy ion collisions

Shaowei Lan·Zi-Wei Lin·Shusu Shi·Xu Sun
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Abstract

In non-central relativistic heavy ion collisions, the created matter possesses a large initial orbital angular momentum. Particles produced in the collisions could be polarized globally in the direction of the orbital angular momentum due to spin-orbit coupling. Recently, the STAR experiment has presented polarization signals for $Λ$ hyperons and possible spin alignment signals for $ϕ$ mesons. Here we discuss the effects of finite coverage on these observables. The results from a multi-phase transport and a toy model both indicate that a pseudorapidity coverage narrower than $|η|< \sim 1$ will generate a larger value for the extracted $ϕ$-meson $ρ_{00}$ parameter; thus a finite coverage can lead to an artificial deviation of $ρ_{00}$ from 1/3. We also show that a finite $η$ and $p_T$ coverage affect the extracted $p_H$ parameter for $Λ$ hyperons when the real $p_H$ value is non-zero. Therefore proper corrections are necessary to reliably quantify the global polarization with experimental observables.

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Shaowei Lan, Zi-Wei Lin, Shusu Shi, Xu Sun. 2018-03-01. Effects of finite coverage on global polarization observables in heavy ion collisions. https://doi.org/10.1016/j.physletb.2018.02.076

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