Explain the mechanism of hyperon transverse polarization

Explain the mechanism responsible for transverse polarization of Lambda hyperons with respect to the production plane in proton-nucleus and related collisions, including its dependence on Feynman-$x$.

Background

At low collision energies, transverse polarization relative to the production plane may contribute substantially to the measured global polarization because the production plane and reaction plane are correlated by large directed flow. Model estimates suggest that this contribution could reach approximately 20 percent at 3 GeV. Although Lambda transverse polarization was observed in pBe collisions as early as 1976, the paper states that its underlying mechanism remains unresolved.