Spin alignment measurements of the K*0(892) and phi (1020) vector mesons in heavy ion collisions at s(NN)**(1/2) = 200 GeV
Phys.Rev.C 77 (2008) 061902, 2008.
The STAR collaboration

Abstract (data abstract)
We present the first spin alignment measurements for the $K^{*0}(892)$ and $\phi(1020)$ vector mesons produced at midrapidity with transverse momenta up to 5 GeV/$c$ at $\sqrt{s_{NN}}=200$ GeV at RHIC. The diagonal spin-density matrix elements with respect to the reaction plane in $Au+Au$ collisions are $\rho_{00}=0.32 \pm 0.04 (\mbox{stat}) \pm 0.09 (\mbox{sys})$ for the $K^{*0}$ ($0.8 < p_{T} < 5.0$ GeV/$c$) and $\rho_{00}=0.34 \pm 0.02 (\mbox{stat}) \pm 0.03 (\mbox{sys})$ for the $\phi$ ($0.4 < p_{T} < 5.0$ GeV/$c$) and are constant with transverse momentum and collision centrality. The data are consistent with the unpolarized expectation of 1/3 and thus no evidence is found for the transfer of the orbital angular momentum of the colliding system to the vector-meson spins. Spin alignments for $K^{*0}$ and $\phi$ in $Au+Au$ collisions were also measured with respect to the particle’s production plane. The $\phi$ result, $\rho_{00}=0.41 \pm 0.02 (\mbox{stat}) \pm 0.04 (\mbox{sys})$, is consistent with that in $p+p$ collisions, $\rho_{00}=0.39 \pm 0.03 (\mbox{stat}) \pm 0.06 (\mbox{sys})$, also measured in this work. The measurements thus constrain the possible size of polarization phenomena in the production dynamics of vector mesons.

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