Azimuthal asymmetries in production of charged hadrons by high energy muons scattered off polarised deuterons at COMPASS

Azimuthal asymmetries in semi-inclusive production of charged hadrons by muons scattered off longitudinally polarised deuterons have been searched for in the COMPASS experiment at CERN. The asymmetries are parameterised taking into account possible contributions from different nucleon parton distribution functions depending on the transverse or longitudinal components of the quark spin and parton fragmentation functions. They can be modulated with sin (φ), sin (2φ), sin (3φ) and cos (φ). The parameterisation includes also a φ- independent term. The amplitudes of all φ-modulation terms for hadrons integrated over kinematic variables are found to be consistent with zero, while the φ-independent terms are non zero and about equal for positive and negative hadrons. The dependence of the parameterization parameters on the kinematic variables x, z and h T p is also studied. The x-dependence of the φ- independent term is found to be in agreement with the COMPASS data on the hadron asymmetry .The x-dependence of the sin (φ) modulation amplitude is observed while dependence of other modulation amplitudes is consistent with no variation vs. the kinematic variables. () h d Ax