Transverse momentum and azimuthal angle distributions of hadrons in DIS at COMPASS

Abstract

The COMPASS experiment plays an important role in studies of nucleon structure. Measurements performed in 2016-2017 with an unpolarised liquid hydrogen target and a longitudinally polarised 160 GeV/$c$ muon beam provide a high-statistics data sample for the analysis of semi-inclusive deep-inelastic scattering, giving access to transverse-momentum-dependent parton distribution and fragmentation functions. The 2016 data set was analysed to determine the multiplicities of hadrons produced in DIS differential in $x$, $Q^2$ and $P_\text{T}$, as well as the amplitudes of azimuthal modulations in the hadron azimuthal-angle distributions. In particular, the unpolarised asymmetries $A^{\cos ϕ_\text{h}}_\text{UU}$ (related to the Cahn effect), $A^{\cos 2ϕ_\text{h}}_\text{UU}$ (sensitive to the Boer--Mulders function), and the beam-spin asymmetry $A^{\sin ϕ_\text{h}}_\text{LU}$ were extracted in 4-dimensional bins matching those of the multiplicities, and also integrated over some of the variables.