Transverse polarization of Lambda and (Lambda)over-bar hyperons in quasireal photoproduction

The HERMES experiment has measured the transverse polarization of Λ and Λ̄ 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 Λ̄ 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 PnΛ̄=-0.025±0.015(stat)±0.018(syst) for Λ and Λ̄, respectively. The dependences of PnΛ and PnΛ̄ on the fraction ζ of 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. © 2007 The American Physical Society.