Abdulhamid, M. I. ; Galatyuk, Tetyana ; Harabasz, Szymon ; Seck, Florian
Hrsg.: STAR Collaboration (2023)
Global polarization of Λ and Λ¯ hyperons in Au+Au collisions at √sNN = 19.6 and 27 GeV.
In: Physical Review C, 108 (1)
doi: 10.1103/PhysRevC.108.014910
Artikel, Bibliographie

Kurzbeschreibung (Abstract)

In relativistic heavy-ion collisions, a global spin polarization, PH, of Λ and ¯Λ hyperons along the direction of the system angular momentum was discovered and measured across a broad range of collision energies and demonstrated a trend of increasing PH with decreasing √sNN. A splitting between Λ and ¯Λ polarization may be possible due to their different magnetic moments in a late-stage magnetic field sustained by the quark-gluon plasma which is formed in the collision. The results presented in this study find no significant splitting at the collision energies of √sNN=19.6 and 27 GeV in the BNL Relativistic Heavy Ion Collisions Beam Energy Scan Phase II using the STAR detector, with an upper limit of P¯Λ−PΛ<0.24% and P¯Λ−PΛ<0.35%, respectively, at a 95% confidence level. We derive an upper limit on the naive extraction of the late-stage magnetic field of B<9.4×1012 T and B<1.4×1013 T at √sNN=19.6 and 27 GeV, respectively, although more thorough derivations are needed. Differential measurements of PH were performed with respect to collision centrality, transverse momentum, and rapidity. With our current acceptance of |y|<1 and uncertainties, we observe no dependence on transverse momentum and rapidity in this analysis. These results challenge multiple existing model calculations following a variety of different assumptions which have each predicted a strong dependence on rapidity in this collision-energy range.

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