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

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.

Non-perturbative structure of the polarized nucleon sea

We investigate the flavour and quark-antiquark structure of the polarized nucleon by calculating the parton distribution functions of the nucleon sea using the meson cloud model. We find that the SU(2) flavor symmetry in the light antiquark sea and quark-antiquark symmetry in the strange quark sea are broken, {\it i.e.} \Delta\ubar < \Delta \dbar and \Delta s < \Delta \sbar. The polarization of the strange sea is found to be positive, which is in contradiction to previous analyses. We predict a much larger quark-antiquark asymmetry in the polarized strange quark sea than that in the unpolarized strange quark sea. Our results for both polarized light quark sea and polarized strange quark sea are consistent with the recent HERMES data.Comment: RevTex, 17 pages plus 8 PS figure

Spin dependent structure function g1g_1 at small xx and small Q2Q^2

Theoretical expectations concerning the low $x$ and low $Q^2$ behaviour of $g_1$ are summarized and compared with the recent SMC data.Comment: 4 pages, plain LATEX, 1 eps figure; contribution to 3rd UK Phenomenology Workshop on HERA Physics, St. John's College, Durham, UK, September 199

A new approach to calculate the gluon polarization

We derive the Leading-Order master equation to extract the polarized gluon distribution G(x;Q^2) = x \deltag(x;Q^2) from polarized proton structure function, g1p(x;Q^2). By using a Laplace-transform technique, we solve the master equation and derive the polarized gluon distribution inside the proton. The test of accuracy which are based on our calculations with two different methods confirms that we achieve to the correct solution for the polarized gluon distribution. We show that accurate experimental knowledge of g1p(x;Q^2) in a region of Bjorken x and Q^2, is all that is needed to determine the polarized gluon distribution in that region. Therefore, to determine the gluon polarization \deltag /g,we only need to have accurate experimental data on un-polarized and polarized structure functions (F2p (x;Q^2) and g1p(x;Q^2)).Comment: 12 pages, 5 figure

Spin dependent structure function g_1 at low x and low Q^2

Theoretical description of the spin dependent structure function g_1(x,Q^2) in the region of low values of x and Q^2 is presented. It contains the Vector Meson Dominance contribution and the QCD improved parton model suitably extended to the low Q^2 domain. Theoretical predictions are compared with the recent experimental data in the low x, low Q^2 region

The connection between single transverse spin asymmetries and the second moment of g2g_2

We point out that the size of the photon single spin asymmetry in high--energy proton proton collisions with one transversely polarized proton can be related to $d^{(2)}$, the twist three contribution to the second moment of $g_2$. Both quantities should be measured in the near future. The first was analysed by Qiu and Sterman, the second was estimated by Balitsky, Braun, and Kolesnichenko. Both experiments measure effectively the strength of the collective gluon field in the nucleon oriented relative to the nucleon spin. The sum rule results suggest that the single spin asymmetry is rather small for the proton, but could be substantial for the neutron.Comment: 6 pages, UFTP preprint 348/199

Can the polarization of the strange quarks in the proton be positive ?

Recently, the HERMES Collaboration at DESY, using a leading order QCD analysis of their data on semi-inclusive deep inelastic production of charged hadrons, reported a marginally positive polarization for the strange quarks in the proton. We argue that a non-negative polarization is almost impossible.Comment: 6 pages, latex, minor changes in the discussion after Eq. (9