| Azimuthal asymmetries in semi-inclusive production of positive (h+) and negative hadrons (h−) have
been measured by scattering 160 GeV muons off longitudinally polarised deuterons at CERN. The
asymmetries were decomposed in several terms according to their expected modulation in the azimuthal
angle f of the outgoing hadron. Each term receives contributions from one or several spin
and transverse-momentum-dependent parton distribution and fragmentation functions. The amplitudes
of all f -modulation terms of the hadron asymmetries integrated over the kinematic variables
are found to be consistent with zero within statistical errors, while the constant terms are nonzero
and equal for h+ and h− within the statistical errors. The dependencies of the f -modulated terms
versus the Bjorken momentum fraction x, the hadron fractional momentum z, and the hadron transverse
momentum pTh
were studied. The x dependence of the constant terms for both positive and
negative hadrons is in agreement with the longitudinal double-spin hadron asymmetries, measured in
semi-inclusive deep-inelastic scattering. The x dependence of the sinf -modulation term is less pronounced
than that in the corresponding HERMES data. All other dependencies of the f -modulation
amplitudes are consistent with zero within the statistical errors. |
