Abstract
We present the first spin alignment measurements for the vector mesons K*0(892) and ϕ(1020) at mid-rapidity in Au+Au and p+p collisions at GeV. Vector mesons appear to be produced without a strong spin alignment constraining possible spin transfer processes from a large orbital angular momentum of the colliding system as expected in theoretical calculations. The diagonal spin density matrix elements are measured to be ρ00 = 0.32 ± 0.04 (stat) ± 0.09 (syst) for the K*0 (0.8 < pT < 5.0 GeV/c) and ρ00 = 0.34 ± 0.02 (stat) ± 0.03 (syst) for the ϕ (0.4 < pT < 5.0 GeV/c), with respect to the reaction plane in midcentral Au+Au collisions, and are found to be independent of collision centrality and transverse momentum. ρ00 with respect to the production plane is measured to be less than 2σ deviation above 1/3 in both Au+Au and p+p collisions indicating the absence of polarization phenomena in the production dynamics for vector mesons in the measured kinematic region.
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