Transverse polarizaton of Λ and anti Λ hyperons in quasireal photoproduction

The HERMES experiment has measured the transverse polarization of Λ and anti Λ hyperons produced inclusively in quasireal photoproduction at a positron beam energy of 27.6 GeV. The transverse polarization PnΛ of the Λ hyperon is found to be positive while the observed anti Λ polarization is compatible with zero. The values averaged over the kinematic acceptance of HERMES are PnΛ = 0.078 ± 0.006 (stat) ± 0.012 (syst) and PnantiΛ = -0.025 ± 0.015 (stat) ± 0.018 (syst) for Λ and anti Λ, respectively. The dependences of PnΛ and PnantiΛ on the fraction of ζ the beam's light-cone momentum carried by the hyperon and on the hyperon's transverse momentum pT were investigated. The measured Λ polarization rises linearly with pT and exhibits a different behavior for low and high values of ζ, which approximately correspond to the backward and forward regions in the center-of-mass frame of the γ*N reaction. (orig.)