Abstrakt
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 cosφhcosφh modulation, the cos2φhcos2φh term related to the Boer-Mulders PDF and sinφhsinφh 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.