We report measurements of inclusive Λ polarization, produced by unpolarized protons incident at several momenta (20, 24, and 28.5 GeV/c) onto hydrogen, deuterium, and beryllium targets. A large polarization from hydrogen, P = -0.34 ± 0.06 at pT = 1.2 GeV/c, establishes the fact that inclusive Λ polarization arises from p-p collisions.
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We would like to thank the staff of the Accelerator Department of Brookhaven National Laboratory for their help. This work was supported in part by the National Science Foundation and in the other part by the Department of Energy.