Nucleon longitudinal spin structure at COMPASS

The nucleon spin structure is studied at COMPASS via the measurement of the spin dependent properties of deep inelastic muon-deuteron scattering. Both inclusive and semi-inclusive observables are investigated, with the emphasis put on the latter. This allows to access, in particular, the gluon polarization ($\Delta G/G$) and the flavor decomposition of the quark helicity distributions. Results from measurements with longitudinal target polarization are presented, as well as uncertainties expected from the first 3 years of data taking.Comment: 4 pages, 2 figures. Prepared for 10th International Baryons Conference (Baryons 2004). To be published with the conference proceedings in Nuclear Physics

Spin structure function g_1 at low x: status and plans

A brief review of measurements and expectations concerning the spin structure function g_1 of the nucleon at low values of the scaling variable x is given.Comment: 4 pages, 3 figures. Invited talk presented at the ``International Workshop on the Spin Structure of the Proton and Polarized Collider Physics'', ECT*, Trento, Italy, July 23-28, 200

Delta G from high pT events at SMC and high pT analysis at COMPASS

Measurements of the longitudinal spin cross section asymmetry for deep inelastic muon-nucleon interactions with two high transverse momentum hadrons ($p_T >$ 0.7 GeV) in the final state are presented for SMC data for polarized proton and deuteron and for data on polarized deuteron from COMPASS taken in 2002 and 2003. The muon asymmetries determined with a cut on $Q^2>$ 1 GeV$^2$ in SMC are: $A_p = 0.03 \pm 0.057\pm 0.01$ and $A_d = 0.070 \pm 0.076 \pm 0.010$, respectively. From these values a gluon polarization $\Delta G /G = -0.20\pm 0.28\pm 0.10$ was obtained at an average fraction of nucleon momentum carried by gluons $\eta = 0.07$. The measured asymmetry (with cut on $Q^2>$ 1 GeV$^2$) in COMPASS is $(A_d/D) = -0.015 \pm 0.08 \pm 0.013$ where D is depolarization factor and the gluon polarization $\Delta G /G = 0.06\pm 0.31\pmComment: 4 pages, 3 figures, Talk given at 10-th International Conference Baryons04, October 25-29, 2004, Ecole Polytechnique, Palaiseau, Franc

GRSV parton densities revisited

An updated next-to-leading order (NLO) QCD analysis of all presently available longitudinally polarized deep-inelastic scattering (DIS) data is presented in the framework of the radiative parton model.Comment: 3 pages, LaTeX, 2 eps figures, uses amssymb, npb (included), and epsfig styles; Contribution to the Proceedings of the 7th International Workshop on `Deep Inelastic Scattering and QCD (DIS99)' [Nucl. Phys. B (Proc. Suppl.)], Zeuthen, Germany, April 199

Results on the nucleon spin structure

SMC performed an investigation of the spin structure of the nucleon by measuring deep inelastic scattering of polarised muons off polarised protons and deuterons. A summary of the results for spin structure functions and sum rules is given.Comment: 8 pages, LaTeX, Talk given at the Workshop on "Symmetry and Spin - PRAHA98", Prag, September 1998. Proceedings to be published by Czech. Journ. Phy

Search for Anomaly at High x in Polarized Deep Inelastic Scattering Data

An idea of possible anomalous contribution of non-perturbative origin to the nucleon spin was examined by analysing data on spin asymmetries in polarized deep inelastic scattering of leptons on nucleons. The region of high Bjorken x was explored. It was shown that experimental data available at present do not evidence for this effect.Comment: Submitted to Mod.Phys.Lett.