Abstract
The recent measurements of the global polarization and vector meson spin alignment along the system orbital momentum in heavy ion collisions are briefly reviewed. A possible connection between the global polarization and the chiral anomalous effects is discussed along with possible experimental checks. Future directions, in particular those aimed on the detailed mapping of the vorticity fields, are outlined. The Blast Wave model is used for an estimate of the anisotropic flow effect on the vorticity component along the beam direction. We also point to a possibility of a circular pattern in the vorticity field in asymmetric, e.g. Cu+Au, central collisions.
Highlights
The idea of the global polarization in heavy ion collisions, the phenomenon characterized by the polarization of the secondary particles along the global system orbital momentum, is almost 15 years old
The progress in vector spin alignments measurements was presented at this conference in talks by the STAR and ALICE Collaborations [10, 11]
The uncertainties in these measurements are still relatively large, and the results are rather inconclusive; below I concentrate on the discussion of the global polarization results
Summary
The idea of the global polarization in heavy ion collisions, the phenomenon characterized by the polarization of the secondary particles along the global system orbital momentum, is almost 15 years old It went “on-shell” in 2004 [1, 2] with the initial predictions for the hyperon polarization as high as “in the order of tens of a percent” [1]. To measure the hyperon global polarization or vector meson spin alignment experimentally, one can either analyze directly the distributions in θ∗, or, in case of the global polarization direction defined by the one of the flow event planes, analyze the azimuthal distribution of the decay products (in the resonance rest frame) relative to that flow plane. For the spin alignment measurements it is possible to use the second order event plane (which typically has much better resolution)
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