Polarization of ( ) Hyperons along the Beam Direction in Collisions at
The Λ ($$\bar{Λ}$$) hyperon polarization along the beam direction has been measured in Au+Au collisions at $$\sqrt{s_{NN}}$$=200 GeV, for the first time in heavy-ion collisions. The polarization dependence on the hyperons' emission angle relative to the elliptic flow plane exhibits a second harmonic sine modulation, indicating a quadrupole pattern of the vorticity component along the beam direction, expected due to elliptic flow. The polarization is found to increase in more peripheral collisions, and shows no strong transverse momentum ($$p_{T}$$) dependence at $$p_{T}$$ greater than 1 GeV/c. Furthermore, the magnitude of the signal is about 5 times smaller than those predicted by hydrodynamic and multiphase transport models; the observed phase of the emission angle dependence is also opposite to these model predictions. In contrast, the kinematic vorticity calculations in the blast-wave model tuned to reproduce particle spectra, elliptic flow, and the azimuthal dependence of the Gaussian source radii measured with the Hanbury Brown-Twiss intensity interferometry technique reproduce well the modulation phase measured in the data and capture the centrality and transverse momentum dependence of the polarization signal.
- Research Organization:
- Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States); Texas A & M Univ., College Station, TX (United States); Brookhaven National Laboratory (BNL), Upton, NY (United States); Stony Brook Univ., NY (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Nuclear Physics (NP); National Science Foundation (NSF); Ministry of Education and Science of the Russian Federation; National Natural Science Foundation of China (NSFC); Chinese Academy of Sciences (CAS); Ministry of Science and Technology of the People’s Republic of China; Ministry of Education of China; National Research Foundation of Korea (NRF); Czech Science Foundation (GACR); Ministry of Education, Youth and Sports of the Czech Republic; Hungarian National Research, Development and Innovation Office (NRDI); Hungarian Ministry of Human Capacities; Government of India; National Science Centre of Poland (NCN); Ministry of Science, Education and Sports of the Republic of Croatia; ROSATOM of Russia; German Federal Ministry of Education and Research (BMBF)
- Contributing Organization:
- STAR Collaboration
- Grant/Contract Number:
- AC02-05CH11231; SC0015636; SC0012704; SC0017982; FG02-87ER40331
- OSTI ID:
- 1574337
- Alternate ID(s):
- OSTI ID: 1524566; OSTI ID: 1594831; OSTI ID: 1787580
- Report Number(s):
- BNL-211736-2019-JAAM; PRLTAO; ark:/13030/qt42f564g6; TRN: US2100195
- Journal Information:
- Physical Review Letters, Vol. 123, Issue 13; ISSN 0031-9007
- Publisher:
- American Physical Society (APS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Local spin polarization in high energy heavy ion collisions
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journal | October 2019 |
Local spin polarization in high energy heavy ion collisions | text | January 2019 |
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