Abstract
Eight proton transverse-spin-dependent azimuthal asymmetries are extracted in four regions of the photon virtuality Q2 from the COMPASS 2010 semi-inclusive hadron measurements in deep inelastic muon–nucleon scattering. These Q2 regions correspond to the four regions of the di-muon mass Q2 used in the ongoing analyses of the COMPASS Drell–Yan measurements, which allows for a future direct comparison of the nucleon transverse-momentum-dependent parton distribution functions extracted from these two alternative measurements. In addition, for the azimuthal asymmetries induced by the Sivers transverse-momentum-dependent parton distribution function various two-dimensional kinematic dependences are presented. The integrated Sivers asymmetries are found to be positive with an accuracy that appears to be sufficient to test the sign change of the Sivers function predicted by Quantum Chromodynamics.
Highlights
Parton distribution functions (PDFs) play a very important role in the theoretical description of high energy reactions
The COMPASS experiment at CERN [17,18] is presently the only place to explore the transverse spin structure of the nucleon by either SIDIS or DY measurements, using a similar set-up and a similar transversely polarised proton target. This opens the unique opportunity, when comparing the Sivers TMD PDFs obtained from the two alternative experimental approaches, to test the oppositesign prediction by Quantum Chromodynamics (QCD) at practically the same hard scale, thereby minimising possible bias introduced by TMD evolution
The analysis presented in this Letter is performed using COMPASS SIDIS data collected in 2010 using a 160 GeV/c longitudinally polarised muon beam from the CERN SPS and a transversely polarised NH3 target with proton polarisation P T ≈ 0.8 and dilution factor f ≈ 0.15, where the latter describes the fraction of polarisable nucleons in the target
Summary
Parton distribution functions (PDFs) play a very important role in the theoretical description of high energy reactions. The COMPASS experiment at CERN [17,18] is presently the only place to explore the transverse spin structure of the nucleon by either SIDIS or DY measurements, using a similar set-up and a similar transversely polarised proton target This opens the unique opportunity, when comparing the Sivers TMD PDFs obtained from the two alternative experimental approaches, to test the oppositesign prediction by QCD at practically the same hard scale, thereby minimising possible bias introduced by TMD evolution. Range iv) is suited to study the predicted sign change of the Sivers TMD PDF when comparing SIDIS and DY results This range best fulfils the requirement of TMD factorisation that the transverse momentum of the hadron in SIDIS or of the muon pair in DY has to be much smaller than Q.
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