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

No abstract

No abstract

A large apparent violation of the OZI rule has recently been found in many channels inpp annihilation at LEAR. An interpretation of these data in terms of the "shakeout" and "rearrangement" of an intrinsicss component of the nucleon wave function is proposed. This gives a channel-dependent, non-universal modification of the naïve OZI prediction. Within this approach, we interpret the strong excess of φ production in S-wavepp annihilations in terms of the polarization of the nucleon'sss component indicated by deep inelastic lepton-nucleon scattering experiments. This interpretation could be tested by measurements of the f ′ 2 (1525)/f 2 (1270) production ratio in P-wave annihilations and by experiments with polarized beams and polarized targets. We also propose a test of the intrinsic strangeness hypothesis in φ production in high-momentum transfer processes, via a difference in constituent counting rules from gluon-mediated production.

No abstract