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Paper proposal global polarization in isobar collisions webpage

Updated on Fri, 2025-02-21 03:56. Originally created by xgou on 2023-12-01 00:33.

 

STAR Paper Proposal

Measurements of global polarization of Lambda (anti-Lambda) and Xi- (Xi+) hyperons in isobar collisions at sqrt(s_NN) = 200 GeV

General information
Title: Measurements of global polarization of Lambda (anti-Lambda) and Xi- (Xi+) hyperons in isobar collisions at sqrt(s_NN) = 200 GeV 
Principal Authors: Xingrui Gou (Shandong), Takafumi Niida (Tsukuba), Sergei A. Voloshin (WSU), Zhenyu Chen (Shandong), Qinghua Xu (Shandong)
Target Journal: PLB

GPC members:

Chairperson: Aihong Tang
Member(s) at large: Yaping Wang
Member for English/Grammar QA: Renee Fatemi
Member for Code QA: Qiang Hu
PWG representative: Subhash Singh
PA representative(s): Xingrui Gou

Previous study: 
https://drupal.star.bnl.gov/STAR/blog/xgou/global-polarization-lambda-and-xi-isobar-phase2-blinded-data-run18
https://drupal.star.bnl.gov/STAR/blog/xgou/update-%CE%BB-%CE%BE-global-polarization-isobar-200gev2018-phase2
https://drupal.star.bnl.gov/STAR/blog/xgou/star-fcv-meetingisobar-run-qa
https://drupal.star.bnl.gov/STAR/blog/xgou/lambda-global-polarization-isobar-ew-epd-effect
https://drupal.star.bnl.gov/STAR/blog/xgou/update-lambda-polarization-isobar-data
https://drupal.star.bnl.gov/STAR/blog/xgou/update-lambda-global-polarization-isobar-fcv-meeting-1110
https://drupal.star.bnl.gov/STAR/blog/xgou/Xi-global-polarization-Isobar-data-FCV-20211215
https://drupal.star.bnl.gov/STAR/blog/xgou/Global-polarization-pt-dependence-check-Isobar-0
https://drupal.star.bnl.gov/STAR/blog/xgou/Updates-global-polarization-hyperons-isobar-collisions-0
https://drupal.star.bnl.gov/STAR/blog/xgou/Paper-Proposal-global-polarization-isobar-slides

Abstract


The polarization of $\Lambda$, $\bar{\Lambda}$, $\Xi^-$ and $\bar{\Xi}^+$ hyperons along the angular momentum of the system has been measured in Ru+Ru and Zr+Zr isobar collisions at \snn = 200 GeV with the STAR detector at RHIC. The polarization dependence on collision centrality was explored for both species and  found to increase in more peripheral collisions. Dependencies on transverse momentum $p_{\rm T}$ and $\eta$ were investigated for $\Lambda$ and $\bar{\Lambda}$ hyperons, but no significant correlation has been observed. For the first time, the dependence of the polarization on the hyperon's emission azimuthal angle with respect to the second harmonic event plane is extracted and shows stronger polarization for the in-plane emitted hyperons at the level of 2.4$\sigma$ significance. The polarization measurements for $\Lambda$ and $\bar{\Lambda}$ are consistent with each other and show no obvious dependence on species or system size. The results for $\Lambda$ hyperons measurements are quantitatively consistent with hydrodynamic calculations incorporating effects from shear-induced polarization and thermal vorticity. $\Xi$ hyperons exhibit a finite positive polarization (2.9$\sigma$ significance) slightly enhanced compared to the inclusive $\Lambda$ polarization.

Proposed figures

Figure 3

Fig.3: Global polarization of Lambda and AntiLambda  as a function of centrality in Ru+Ru & Zr+Zr collisions at sqrt(s_NN)=200 GeV. Open boxes and vertical lines show systematic and statistical uncertainties, respectively.

Figure 4



Fig.4: Global Polarization of Λ+anti-Λ as a function of centrality in Ru+Ru and Zr+Zr collisions at sqrt(s_NN)=200 GeV. Open boxes and vertical lines show systematic and statistical uncertainties, respectively. Results for the Λ and anti-Λ measurements in Au+Au collisions at sqrt(s_NN)=200 GeV are shown for comparison.

Figure 5，6



Fig.5，6 : Polarization of Λ+anti-Λ as a function of p_T and eta for the 20%-60% centrality in Ru+Ru & Zr+Zr collisions at sqrt(s_NN)=200 GeV.  Open boxes and vertical lines show systematic and statistical uncertainties, respectively. Results for the Λ + anti-Λ measurements in Au+Au collisions at sqrt(s_NN)=200 GeV are shown for comparison.

 

Figure 7，8



Fig.7，8 : P_{y,c0} and P_{y,c2} of Λ+anti-Λ as a function of centrality in Ru+Ru&Zr+Zr collisions at sqrt(s_NN)=200 GeV. Open boxes and vertical lines show systematic and statistical uncertainties, respectively.

 

Figure 9


Fig.9 : The global polarization of Ξ-+Ξ+  hyperons obtained via measurements of the polarization of daughter Lambda hyperons and direct measurements as a function of the centrality bins in isobar collisions at sqrt(s_NN)=200 GeV. Results for Ξ-+Ξ+  in Au+Au collisions at sqrt(s_NN)=200 GeV are shown for comparison.

 
Summary

We presented the results of global polarization measurements for $\Lambda$, $\bar\Lambda$, $\Xi^-$, and $\Xi^+$ hyperons in Ru+Ru and Zr+Zr collisions at \snn = 200 GeV. $\Lambda$+$\bar\Lambda$ global polarization are consistent between isobar and Au+Au collisions, indicating no obvious collision system size dependence. Within the uncertainties, our results agree with calculations from hydrodynamic models. No significant difference between $\Lambda$ and $\bar\Lambda$ global polarization in Ru+Ru and Zr+Zr collisions is observed, consitent with no magnetic-field-driven effects on the observed hyperon polarization within present statistical precision. The polarization was also studied as a functions of the collision centrality, the hyperon's transverse momentum, pseudorapidity, and azimuthal angle. The polarization was found to increase towards peripheral collisions, as expected from theoretical calculations, but shows no significant dependence on pseudorapidity or transverse momentum. The results on azimuthal angle dependence indicates larger polarization in the in-plane direction with 2.4$\sigma$ significance. Furthermore, $\Xi^-$ and $\Xi^+$ hyperon global polarization via the measurement of daughter \lam polarization indicates positive polarization as expected from the global vorticity picture. 

 


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