Abstract
In non-central nuclear collisions, the created matter should exhibit strong vorticity, which induces spin polarization. Global polarization is a good tool to investigate the dynamics of the system. Global polarization of Λ and Λ¯ hyperons has been measured at √SNN = 2.4 GeV - 5.02 TeV in various experiments. We have measured the global polarization of Λ hyperons in Au+Au collisions with fixed-target configuration at √SNN = 7.2 GeV at RHIC-STAR experiment. The non-zero signal is observed and it follows the global trend of Λ global polarization that increases towards lower collision energies. The global polarization is larger in more peripheral collisions but it does not show any significant rapidity dependence as well as transverse momentum dependence within uncertainties.
Highlights
In non-central heavy-ion collisions, the created matter should exhibit a rotational motion because of the conservation of the initial orbital angular momentum carried by the two nuclei, which is perpendicular to the reaction plane
Since the system angular momentum is perpendicular to the reaction plane, the global polarization can be measured via the distribution of the azimuthal angle of the daughter proton in the Λ’s rest frame with respect to the reaction plane as follows [2]:
We present the first measurement of Λ global polarization in Au+Au collisions at √sNN = 7.2 GeV with STAR fixed-target configuration
Summary
In non-central heavy-ion collisions, the created matter should exhibit a rotational motion because of the conservation of the initial orbital angular momentum carried by the two nuclei, which is perpendicular to the reaction plane. 7.T7h-e2S00TAGReVCaonlldaboobrsaetrivoendrpeopsoirtitveed stihgenagllso[b2a–l 4].√the ALICE Collaboration measured global polarization of Λ and Λhyperons at sNN = 2.76, 5.02 TeV [5]. The daughter particles were identified using TPC dE/dx and TOF and Λ hyperons were reconstructed based on the invariant mass, applying cuts on decay topology. In this parity-violating weak decay, the daughter proton preferentially decays along the Λ’s spin direction. Since the system angular momentum is perpendicular to the reaction plane, the global polarization can be measured via the distribution of the azimuthal angle of the daughter proton in the Λ’s rest frame with respect to the reaction plane as follows [2]:. Fsiiognusreat1:√IsnNvNar=ia7n.t2mGaesVs .distribution of Λ hyperons in 0%-80% centrality for Au+Au colli-
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