Azimuthal Asymmetries in Unpolarised Semi-Inclusive DIS at COMPASS

In semi-inclusive deep inelastic scattering (SIDIS) the non-zero transverse momentum of partons induces azimuthal dependence of the cross-section. For an unpolarised nucleon, three azimuthal modulations that can be related to different combinations of twist-two or higher-twist transverse momentum dependent PDFs and fragmentation functions arise: the so-called Cahn effect reflected in a \(\cos \varphi _{\text{h}}\) modulation, the \(\cos 2\varphi _{\text{h}}\) term related to the Boer–Mulders PDF and \(\sin \varphi _{\text{h}}\) effect known as beam-spin asymmetry. In 2016 and 2017, the COMPASS experiment at CERN collected a large sample of SIDIS events using a longitudinally polarised 160 GeV/c muon beam scattering on a liquid hydrogen target. Amplitudes of the aforementioned azimuthal modulations have been extracted from part of the data. A new procedure has been developed to subtract a background coming from the decay of diffractively produced vector mesons. The results presented in this talk qualitatively agree with earlier COMPASS results obtained with an isoscalar target.