Azimuthal asymmetries of charged hadrons produced muons off longitudinally polarised deuterons at COMPASS

Azimuthal asymmetries in semi-inclusive production of positive ($h^{+}$) and negative hadrons ($h^{-}$) have been measured by scattering of 160 GeV muons off longitudinally polarised deuterons at CERN. The asymmetries were decomposed in several terms, according to their expected modulation as a function of the outgoing hadron azimuthal angle $\phi$. Each term receives contributions from one or several spin and transverse-momentum-dependent parton distribution and fragmentation functions. The amplitudes of all $\phi$-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 $\phi$-modulated terms versus the Bjorken momentum fraction $x$, the hadron fractional momentum $z$, and the hadron transverse momentum $p^{h}_{T}$ 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 sin$\phi$-modulation term is less pronounced than that in the corresponding HERMES data. All other dependencies of the $\phi$-modulation amplitudes are consistent with zero within the statistical errors.