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The European Physical Journal A

, Volume 31, Issue 4, pp 620–625 | Cite as

Spin physics at COMPASS

  • J. M. Friedrich
QNP 2006
  • 26 Downloads

Abstract.

Results for the spin structure of the nucleon from the COMPASS data taking periods 2002 to 2004 are presented. The quark contribution to the nucleon spin, following from a QCD fit to the new data, turns out to be significantly larger than it was derived from the previous world data. The new data favour, on the other side, a comparatively small gluon polarisation in the range x g ≈ 0.1. In the data taken with the deuteron target polarised transversely the related asymmetries are found to be small on the level of accuracy reached so far, indicating a cancellation of the proton and neutron contributions. This is in agreement, for both the Collins and the Sivers asymmetry, with recent theoretical calculations. Also, a step towards the understanding of angular-momentum contributions with COMPASS is taken by the evaluation of asymmetries in exclusive vector meson production.

PACS.

25.30.Mr Muon scattering (including the EMC effect) 21.10.Hw Spin, parity, and isobaric spin 24.85.+p Quarks, gluons, and QCD in nuclei and nuclear processes 13.60.-r Photon and charged-lepton interactions with hadrons 

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Copyright information

© Società Italiana di Fisica and Springer-Verlag 2007

Authors and Affiliations

  • J. M. Friedrich
    • 1
  1. 1.Physik DepartmentTechnische Universität MünchenGermany

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