Contribution of exclusive diffractive processes to the measured azimuthal asymmetries in SIDIS
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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 $^6$LiD target. In both cases, the amplitudes of the $\cos\phi_h$ and $\cos 2\phi_h$ 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 $\cos 2\phi_h$ modulation gives indication for a non-zero Boer-Mulders effect.
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Cited by 2 Pith papers
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Measurements of transverse-momentum dependent effects in semi-inclusive DIS at COMPASS
New COMPASS data from polarized deuteron targets reduce uncertainties on d-quark transversity by a factor of 2.5 at large Bjorken x and will enable first extraction of the Boer-Mulders function from unpolarized nucleon data.
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Azimuthal Asymmetries in Unpolarised Semi-Inclusive DIS at COMPASS
COMPASS extracts cos φ_h, cos 2φ_h and sin φ_h azimuthal asymmetries from 2016-2017 muon-hydrogen SIDIS data and reports qualitative agreement with prior isoscalar-target results after a new diffractive vector-meson b...
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