We report on the first measurement of the spin-dependent structure function g1d of the deuteron in the deep inelastic scattering of polarised muons off polarised deuterons, in the kinematical range 0.006

No abstract

The first measurement of transverse-spin-dependent azimuthal asymmetries in the pion-induced Drell-Yan (DY) process is reported. We use the CERN SPS 190  GeV/c π^{-} beam and a transversely polarized ammonia target. Three azimuthal asymmetries giving access to different transverse-momentum-dependent (TMD) parton distribution functions (PDFs) are extracted using dimuon events with invariant mass between 4.3  GeV/c^{2} and 8.5  GeV/c^{2}. Within the experimental uncertainties, the observed sign of the Sivers asymmetry is found to be consistent with the fundamental prediction of quantum chromodynamics (QCD) that the Sivers TMD PDFs extracted from DY have a sign opposite to the one extracted from semi-inclusive deep-inelastic scattering (SIDIS) data. We present two other asymmetries originating from the pion Boer-Mulders TMD PDFs convoluted with either the nucleon transversity or pretzelosity TMD PDFs. A recent COMPASS SIDIS measurement was obtained at a hard scale comparable to that of these DY results. This opens the way for possible tests of fundamental QCD universality predictions.

We present the final results of the spin asymmetries A 1 and the spin structure functions g 1 of the proton and the deuteron in the kinematic range 0.0008ϽxϽ0.7 and 0.2ϽQ 2 Ͻ100 GeV 2 . For the determination of A 1 , in addition to the usual method which employs inclusive scattering events and includes a large radiative background at low x, we use a new method which minimizes the radiative background by selecting events with at least one hadron as well as a muon in the final state. We find that this hadron method gives smaller errors for xϽ0.02, so it is combined with the usual method to provide the optimal set of results.

The COMPASS Collaboration at CERN has measured the transverse spin azimuthal asymmetry of\ud charged hadrons produced in semi-inclusive deep inelastic scattering using a 160 GeV μ+ beam and a\ud transversely polarised NH3 target. The Sivers asymmetry of the proton has been extracted in the Bjorken\ud x range 0.003 < x < 0.7. The new measurements have small statistical and systematic uncertainties of\ud a few percent and confirm with considerably better accuracy the previous COMPASS measurement. The\ud Sivers asymmetry is found to be compatible with zero for negative hadrons and positive for positive\ud hadrons, a clear indication of a spin–orbit coupling of quarks in a transversely polarised proton. As\ud compared to measurements at lower energy, a smaller Sivers asymmetry for positive hadrons is found\ud in the region x > 0.03. The asymmetry is different from zero and positive also in the low x region,\ud where sea-quarks dominate. The kinematic dependence of the asymmetry has also been investigated and\ud results are given for various intervals of hadron and virtual photon fractional energy. In contrast to the\ud case of the Collins asymmetry, the results on the Sivers asymmetry suggest a strong dependence on the\ud four-momentum transfer to the nucleon, in agreement with the most recent calculations