Measurements of local polarization of Λ hyperons with event shape engineering in Au+Au collisions at RHIC-STAR
Abstract
Anisotropic flow is expected to generate local vorticities along the beam direction, which in turn lead to local polarization of produced particles. Although the local polarization of hyperons has already been observed at RHIC and the LHC, its mechanism is not yet understood: model calculations indicate that the shear-induced and vorticity-induced contributions can have opposite signs and may substantially cancel, so that the resulting polarization depends sensitively on the theoretical implementation. Since both are driven by the anisotropic flow, we employ the Event Shape Engineering (ESE) method, which selects events with different flow magnitudes within a narrow centrality range, to measure the local polarization as a function of the elliptic flow at a fixed multiplicity. We report the measurements of the elliptic flow (v2) and the local polarization (Pz,2) of Λ and Λ̅ as a function of the reduced flow vector magnitude q2 used for the ESE event selection, in Au+Au collisions at √(sNN) = 19.6 GeV from the STAR experiment. The v2 shows a clear positive dependence on q2, while Pz,2 indicates a weak positive dependence on q2 and v2. This is the first measurement to directly investigate the relation between anisotropic flow and local polarization, providing new insight into the origin of local polarization.
Versions
Related
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BibTeX
@misc{kondo2026measurements,
title = {{Measurements of local polarization of $Λ$ hyperons with event shape engineering in Au+Au collisions at RHIC-STAR}},
author = {Taiki Kondo},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.25989},
eprint = {2610.25989},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.25989},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Measurements of local polarization of Λ hyperons with event shape engineering in Au+Au collisions at RHIC-STAR
AU - Taiki Kondo
PY - 2026
DA - 2026/10/20
PB - arXiv
DO - 10.48550/arxiv.2610.25989
UR - https://arxiv.org/abs/2610.25989
AB - Anisotropic flow is expected to generate local vorticities along the beam direction, which in turn lead to local polarization of produced particles. Although the local polarization of hyperons has already been observed at RHIC and the LHC, its mechanism is not yet understood: model calculations indicate that the shear-induced and vorticity-induced contributions can have opposite signs and may substantially cancel, so that the resulting polarization depends sensitively on the theoretical implementation. Since both are driven by the anisotropic flow, we employ the Event Shape Engineering (ESE) method, which selects events with different flow magnitudes within a narrow centrality range, to measure the local polarization as a function of the elliptic flow at a fixed multiplicity. We report the measurements of the elliptic flow (v_2) and the local polarization (P_z,2) of Λ and Λ̅ as a function of the reduced flow vector magnitude q_2 used for the ESE event selection, in Au+Au collisions at √(s_NN) = 19.6 GeV from the STAR experiment. The v_2 shows a clear positive dependence on q_2, while P_z,2 indicates a weak positive dependence on q_2 and v_2. This is the first measurement to directly investigate the relation between anisotropic flow and local polarization, providing new insight into the origin of local polarization.
ER -