Transverse polarization of Λ and Λ¯ hyperons in quasireal photoproduction

The HERMES experimenthas measured the transverse polarization of A and A hyperonsproduced inclusively in quasireal photoproduction at a positron beam energy of 27.6 GeV. The transverse polarization P Λ n of the A hyperonis found to be positive while the observed A polarization is compatible with zero. The values averagedover the kinematic acceptance of HERMES are P Λ n = 0.078± 0.006( stat) ± 0.012(syst) and P Λ n = -0.025 ± 0.015( stat) ± 0.018(syst) for A and A, respectively. The dependences of P Λ n and P Λ n on the fraction ζ of the beam's light-conemomentum carried by the hyperonand on the hyperon's transverse momentum p T were investigated. The measured A polarization rises linearly with p T 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.