A single-spin asymmetry in the distribution of exclusively produced pi(+) mesons azimuthally around the virtual photon direction relative to the lepton scattering plane has been measured for the first time in deep-inelastic scattering of positrons off longitudinally polarized protons. Integrated over the experimental acceptance, the sin moment of the polarization asymmetry of the cross section is measured to be -0.18 +/- 0.05(stat.) +/- 0.02(syst.). The asymmetry is also studied as a function of the relevant kinematic variables, and its magnitude is found to grow with decreasing x and increasing -t and vanish at t --> t(min) (where x is the Bjorken scaling variable and t is the squared four-momentum transferred to the nucleon). (C) 2002 Elsevier Science B.V. All rights reserved.
- LEADING ORDER