Spin alignment of vector mesons in unpolarized hadron-hadron collisions at high energies

We argue that the spin alignment of the vector mesons observed in unpolarized hadron-hadron collisions is closely related to the single-spin left-right asymmetry observed in transversely polarized hadron-hadron collisions. We present the numerical results obtained from the type of spin-correlation imposed by the existence of the single-spin left-right asymmetries. We compare the results with the available data and make predictions for future experiments.