Azimuthal single-spin asymmetries of lepto-produced pions and charged kaons were measured on a transversely polarized hydrogen target. Evidence for a naive-T-odd, transverse-momentum-dependent parton distribution function is deduced from non-vanishing Sivers effects for pi+, pi0, and K+, K-, as well as in the difference of the pi+ and pi- cross sections.
@article{arxiv.0906.3918,
title = {Observation of the Naive-T-odd Sivers Effect in Deep-Inelastic Scattering},
author = {The HERMES Collaboration},
journal= {arXiv preprint arXiv:0906.3918},
year = {2012}
}