Paper proposal global polarization in isobar collisions
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:
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
In this letter we report the results of the global polarization measurements of Lambda/Lambda-bar, as well as Xi/Xi-bar hyperons in isobar Ru+Ru and Zr+Zr collisions at sqrt(s) = 200 GeV recorded with STAR at RHIC. The results are presented for different collision centralities, and for Lambda hyperons as functions of transverse momentum (pT) and pseudorapidity (eta) in 20-60% centrality interval. No significant difference has been observed between Lambda and Lambda-bar polarizations providing an upper limit on the values of the magnetic field in the final stages of the collision. The observed polarization increases towards peripheral collisions, with no significant pT, eta, or azimuthal angle dependence. Comparison of the polarization in isobar collision to those to the results in Au+Au collisions reveals no obvious system size dependence expected in some models accounting for interplay between hyperon production time and vorticity time evolution. The hydrodynamic model calculations, accounting for shear induced polarization in either Λ and s-quark polarization scenarios, are both consistent with the experiment data.
Proposed figures
Figure 1
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Fig.1: 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.
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Figure2
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Fig.2: 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 3
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Fig.3 : 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 4
Fig.4 : 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 5
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Fig.5 : 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 present the results of global polarization measurements for Lambda, AntiLambda and Xi-, Xi+ hyperons in Ru+Ru and Zr+Zr collisions at √sNN = 200 GeV. No significant difference between Lambda and AntiLambda global polarization in Ru+Ru and Zr+Zr collisions is observed, indicates that there is no magnetic field driven effects on the hyperon polarization within present statistical precision. Lambda+AntiLambda global polarization are consistent between isobar and Au+Au collisions, indicating there is no obvious collision system size dependence. Within the uncertainties, our results agree with predictions from hydrodynamic (AMPT+MUSIC) models. The polarization was also studied as functions of the conlision 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 no significant dependence on pseudorapidity, transverse momentum or azimuthal angle was observed. Furthermore, no significant Xi− and Xi+ hyperon global polarization signal from direct and indirect measurements, results are consistent.
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