Measurement of longitudinal-target-polarization dependent azimuthal asymmetries in SIDIS at COMPASS experiment

Abstract

Preliminary results obtained by the COMPASS experiment for longitudinal-spin-dependent azimuthal asymmetries in single-hadron muoproduction off protons are presented for the first time. The analysis was carried out on the full data sample collected by COMPASS with longitudinally polarized proton ($NH_3$) target in 2007 and 2011 using 160~\gvc and 200~\gvc muon beams, correspondingly. Within QCD parton model approach extracted asymmetries are giving access to the specific convolutions of certain transverse-momentum-dependent \textit{twist-2} and \textit{higher twist} parton distribution functions and fragmentation functions. In order to access different features of the involved distributions, the asymmetries are extracted as functions of different kinematic variables for both positive and negative single-hadron productions. The significant amount of collected data and wide kinematic range give unique importance to the results. Obtained asymmetries are compared with previous measurements performed by HERMES experiment and with available model predictions.