Effects of transversity in deep-inelastic scattering by polarized protons

Single-spin asymmetries for pions and charged kaons are measured in semi-inclusive deep-inelastic scattering of positrons and electrons off a transversely nuclear-polarized hydrogen target. The dependence of the cross section on the azimuthal angles of the target polarization (phi s) and the produced hadron (phi) is found to have a substantial sin(phi +phi s) modulation for the production of pi(+), pi(-) and K+. This Fourier component can be interpreted in terms of non-zero transversity distribution functions and non-zero favored and disfavored Collins fragmentation functions with opposite sign. For pi(0) and K- production the amplitude of this Fourier component is consistent with zero. (C) 2010 Elsevier B.V. All rights reserved.