Global Polarization of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="normal">Ξ</mml:mi></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="normal">Ω</mml:mi></mml:math> Hyperons in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>Au</mml:mi><mml:mo>+</mml:mo><mml:mi>Au</mml:mi></mml:mrow></mml:math> Collisions at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msqrt><mml:msub><mml:mi>s</mml:mi><mml:mrow><mml:mi>N</mml:mi><mml:mi>N</mml:mi></mml:mrow></mml:msub></mml:msqrt><mml:mo>=</mml:mo><mml:mn>200</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>GeV</mml:mi></mml:math>
J. Adam, L. Adamczyk, J. R. Adams, J. K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, I. Alekseev, D. M. Anderson, A. Aparin, E. C. Aschenauer, M. U. Ashraf, F. G. Atetalla, A. Attri, G. S. Averichev, V. Bairathi, K. N. Barish, A. Behera, R. Bellwied, A. Bhasin, J. Bielčík, J. Bielčíková, L. C. Bland, I. G. Bordyuzhin, J. D. Brandenburg, A. V. Brandin, J. M. Butterworth, H. Caines, M. Calderón de la Barca Sánchez, D. Cebra, I. Chakaberia, P. Chaloupka, B. K. Chan, F-H. Chang, Z. Chang, N. Chankova-Bunzarova, A. Chatterjee, D. Chen, J. Chen, J. H. Chen, Xiang Chen, Z. Chen, J. Cheng, M. Cherney, M. Chevalier, S. Choudhury, W. Christie, X. Chu, H. J. Crawford, M. Csanád, M. Daugherity, T. G. Dedovich, I. M. Deppner, A. A. Derevschikov, L. Didenko, X. Dong, J. L. Drachenberg, J. C. Dunlop, T. Edmonds, N. Elsey, J. Engelage, G. Eppley, S. Esumi, O. Evdokimov, A. Ewigleben, O. Eyser, R. Fatemi, S. Fazio, P. Federic, J. Fedorišin, C. Feng, Y. Feng, P. Filip, E. Finch, Y. Fisyak, A. Francisco, Ł. Fulek, C. A. Gagliardi, T. Galatyuk, F. J. M. Geurts, N. Ghimire, S. M. Gibson, K. Gopal, X. Gou, D. Grosnick, W. Guryn, A. I. Hamad, A. Hamed, S. Harabasz, J. W. Harris, S. He, W. He, X. H. He, Y. He, S. Heppelmann, S. Heppelmann, N. Herrmann, Eric A. Hoffman, L. Holub, Y. Hong
Abstract
Global polarization of $\mathrm{\ensuremath{\Xi}}$ and $\mathrm{\ensuremath{\Omega}}$ hyperons has been measured for the first time in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{{s}_{NN}}=200\text{ }\text{ }\mathrm{GeV}$. The measurements of the ${\mathrm{\ensuremath{\Xi}}}^{\ensuremath{-}}$ and ${\overline{\mathrm{\ensuremath{\Xi}}}}^{+}$ hyperon polarization have been performed by two independent methods, via analysis of the angular distribution of the daughter particles in the parity violating weak decay $\mathrm{\ensuremath{\Xi}}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}+\ensuremath{\pi}$, as well as by measuring the polarization of the daughter $\mathrm{\ensuremath{\Lambda}}$ hyperon, polarized via polarization transfer from its parent. The polarization, obtained by combining the results from the two methods and averaged over ${\mathrm{\ensuremath{\Xi}}}^{\ensuremath{-}}$ and ${\overline{\mathrm{\ensuremath{\Xi}}}}^{+}$, is measured to be $⟨{P}_{\mathrm{\ensuremath{\Xi}}}⟩=0.47\ifmmode\pm\else\textpm\fi{}0.10(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.23(\mathrm{syst})%$ for the collision centrality 20%--80%. The $⟨{P}_{\mathrm{\ensuremath{\Xi}}}⟩$ is found to be slightly larger than the inclusive $\mathrm{\ensuremath{\Lambda}}$ polarization and in reasonable agreement with a multiphase transport model. The $⟨{P}_{\mathrm{\ensuremath{\Xi}}}⟩$ is found to follow the centrality dependence of the vorticity predicted in the model, increasing toward more peripheral collisions. The global polarization of $\mathrm{\ensuremath{\Omega}}$, $⟨{P}_{\mathrm{\ensuremath{\Omega}}}⟩=1.11\ifmmode\pm\else\textpm\fi{}0.87(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}1.97(\mathrm{syst})%$ was obtained by measuring the polarization of daughter $\mathrm{\ensuremath{\Lambda}}$ in the decay $\mathrm{\ensuremath{\Omega}}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}+K$, assuming the polarization transfer factor ${C}_{\mathrm{\ensuremath{\Omega}}\mathrm{\ensuremath{\Lambda}}}=1$.