Investigations of azimuthal asymmetry in semi-inclusive leptoproduction K.A. Oganessyan, H.R. Avakian, N. Bianchi and P. Di Nezza Eur. Phys. J. C, 5 4 (1998) 681-685 Published online: 26 March 1998 DOI: 10.1007/s100529800873