Abstract
A comprehensive collection of results on longitudinal double-spin asymmetries is presented for charged pions and kaons produced in semi-inclusive deep-inelastic scattering of electrons and positrons on the proton and deuteron, based on the full HERMES data set. The dependence of the asymmetries on hadron transverse momentum and azimuthal angle extends the sensitivity to the flavor structure of the nucleon beyond the distribution functions accessible in the collinear framework. No strong dependence on those variables is observed. In addition, the hadron charge-difference asymmetry is presented, which under certain model assumptions provides access to the helicity distributions of valence quarks.
Highlights
Measurements of deep-inelastic scattering (DIS) with both beam and target longitudinally polarized have provided access to the polarization-dependent structure of the nucleon (e.g., Table I of Ref. [1])
While yielding substantial knowledge on the longitudinal momentum and polarization structure of the nucleon, such interpretation excludes the rich phenomenology of transverse-momentum dependent (TMD) parton distribution and fragmentation functions [14,15]
Unlike the case of unfolding of polarizationindependent hadron yields in the measurement of hadron multiplicities [40], which are strongly dependent on the hadron kinematics and which require unfolding in those variables, the dependence of longitudinal double-spin asymmetries on hadron kinematics in this analysis is weak and the unfolding procedure is found to be robust against possible model dependence when performed in only those dimensions presented here, e.g., when the polarizationdependent yields are integrated over z or Ph⊥
Summary
Measurements of deep-inelastic scattering (DIS) with both beam and target longitudinally polarized have provided access to the polarization-dependent structure of the nucleon (e.g., Table I of Ref. [1]). The Ph⊥ dependence of semi-inclusive asymmetries is sensitive to the transverse-momentum contributions from both the partonic structure of the nucleon and the fragmentation process through which final-state hadrons are produced. For the purpose of discussion and comparison some assumptions are made in the analysis, but the leptonnucleon asymmetry Ahk [cf Eq (5)] should be taken to be the primary model-independent observable and is provided in the data tables in all cases This asymmetry differs from AhLL only in the direction in which the nucleon polarization is measured, either with respect to the beam for the former, or with respect to the virtual photon for the latter. In order to relate Ahk to the virtual-photon-nucleon asymmetry Ah1 [cf Eq (6)], a parametrization of the longitudinalto-transverse photoabsorption cross-section ratio R 1⁄4 σL=σT must be assumed To date, this quantity has only been measured in inclusive DIS. In semi-inclusive DIS this ratio might depend strongly on the hadron kinematics, in particular, on Ph⊥
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