Hadron leptoproduction in Semi-Inclusive measurements of Deep-Inelastic Scattering (SIDIS) on unpolarised nucleons allows one to get information on the intrinsic transverse momentum of quarks in a nucleon and on the Boer-Mulders function through the measurement of azimuthal modulations in the cross section. These modulations were recently measured by the HERMES experiment at DESY on proton and deuteron targets, and by the COMPASS experiment using the CERN SPS muon beam and a 6LiD target. In both cases, the amplitudes of the cos⁡ϕh and cos⁡2ϕh modulations show strong kinematic dependences for both positive and negative hadrons. It has been known since some time that the measured final-state hadrons in those SIDIS experiments receive a contribution from exclusive diffractive production of vector mesons, particularly important at large values of z, the fraction of the virtual photon energy carried by the hadron. In previous measurements of azimuthal asymmetries this contribution was not taken into account, because it was not known that it could distort the azimuthal modulations. Presently, a method to evaluate the contribution of the exclusive reactions to the azimuthal asymmetries measured by COMPASS has been developed. The subtraction of this contribution results in a better understanding of the kinematic effects, and the remaining non-zero cos⁡2ϕh modulation gives indication for a non-zero Boer-Mulders effect.

Original languageEnglish
Article number115039
JournalNuclear Physics B
StatePublished - Jul 2020


FundersFunder number
Daiko and Yamada Foundations
National Science FoundationPHY-1506416
National Science Foundation
Seventh Framework Programme1506416, 283286
Seventh Framework Programme
European Commission
Deutsche Forschungsgemeinschaft
Japan Society for the Promotion of Science18002006, 20540299, 26247032, 18540281
Japan Society for the Promotion of Science
Ministry of Education, Culture, Sports, Science and Technology
Ministerstvo Školství, Mládeže a TělovýchovyLM20150581
Ministerstvo Školství, Mládeže a Tělovýchovy
Fundação para a Ciência e a TecnologiaCERN/FIS-PAR/0022/2019, CERN/FIS-PAR/0007/2017
Fundação para a Ciência e a Tecnologia
Bundesministerium für Bildung und Forschung
Israel Academy of Sciences and Humanities0.1764
Israel Academy of Sciences and Humanities
LabexANR-10-LABX-0038, ANR-11-IDEX-0003-01
Narodowe Centrum Nauki2017/26/M/ST2/00498
Narodowe Centrum Nauki
Ministry of Science and Technology, Taiwan


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