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

The momentum and helicity density distributions of the strange quark sea in the nucleon are obtained in leading order from charged-kaon production in deep-inelastic scattering on the deuteron. The distributions are extracted from spin-averaged K� multiplicities, and from K� and inclusive double-spin asymmetries for scattering of polarized positrons by a polarized deuterium target. The shape of the momentum distribution is softer than that of the average of the and quarks. In the region of measurement 0.021.0�GeV2, the helicity distribution is zero within experimental uncertainties

Multiplicities in semi-inclusive deep-inelastic scattering are presented for each charge state of pi(+/-) and K-+/- mesons. The data were collected by the HERMES experiment at the HERA storage ring using 27.6 GeV electron and positron beams incident on a hydrogen or deuterium gas target. The results are presented as a function of the kinematic quantities x(B), Q(2), z, and P-h perpendicular to. They represent a unique data set for identified hadrons that will significantly enhance our understanding of the fragmentation of quarks into final-state hadrons in deep-inelastic scattering. DOI: 10.1103/PhysRevD.87.07402

Azimuthal single-spin asymmetries of leptoproduced 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 nonvanishing Sivers effects for pi(+), pi(0), and K(+/-), as well as in the difference of the pi(+) and pi(-) cross sections.

The azimuthal cos φ and cos 2φ modulations of the distribution of hadrons produced in unpolarized semi-inclusive deep-inelastic scattering of electrons and positrons off hydrogen and deuterium targets have been measured in the Hermes experiment. For the first time these modulations were determined in a four-dimensional kinematic space for positively and negatively charged pions and kaons separately, as well as for unidentified hadrons. These azimuthal dependences are sensitive 2 to the transverse motion and polarization of the quarks within the nucleon via, e.g., the Cahn, Boer-Mulders and Collins effects.

Single-spin asymmetries were investigated in inclusive electroproduction of charged pions and kaons from transversely polarized protons at the HERMES experiment. The asymmetries were studied as a function of the azimuthal angle psi about the beam direction between the target-spin direction and the hadron production plane, the transverse hadron momentum P-T relative to the direction of the incident beam, and the Feynman variable x(F). The sin psi* amplitudes are positive for pi(+) and K+ slightly negative for pi(-) and consistent with zero for K-, with particular P-T but weak x(F) dependences. Especially large asymmetries are observed for two small subsamples of events, where also the scattered electron was recorded by the spectrometer. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved

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The first detailed measurement of the dependence on target nuclear mass of the average squared transverse momentum p 2 t of π + , π − , and K + mesons from deep-inelastic lepton scattering is obtained as a function of several kinematic variables. The data were accumulated at the Hermes experiment at Desy, in which the Hera 27.6 GeV lepton beam was scattered off several nuclear gas targets. The average squared transverse momentum was clearly observed to increase with atomic mass number. The effect increases as a function of Q 2 and x and remains constant as a function of