Polarized Parton Densities in the Nucleon

We present a new NLO QCD analysis of the world data on inclusive polarized deep inelastic scattering. Comparing to our previous analysis: i) the values of g_A and a_8=3F-D are updated ii) the MRST'99 instead of the MRST'98 parametrization for the input unpolarized parton densities is used and iii) the recent SLAC E155 proton data on the spin asymmetry A1 are included in the analysis. A new set of polarized parton densities is extracted from the data and the sensitivity of the results to different positivity constraints is discussed.Comment: 4 pages, 1 figure, LaTeX, typing errors in the numbers for \Delta \Sigma are corrected, talk presented at the 9th International Workshop on Deep Inelastic Scattering and QCD (DIS2001), Bologna, Italy, 27 Apr-1 May 200

Target Mass Effects in Polarized Deep Inelastic Scattering

The target mass effects in polarized DIS have been studied. It was demonstrated that taking into account the first order target mass corrections to g1 a very good approximation of the exact formula is achieved. It was also shown that their magnitude in the preasymptotic DIS region is small except for x > 0.65, where their large effect is partially suppressed by the large values of $Q^2$ due to the cut $W^2 > 4 GeV^2$. The difference between the size of the target mass and higher twist corrections is illustrated.Comment: 8 pages, LaTeX, 5 figures, typo in Eq. 3 corrected, comment added, to appear in Mod. Phys. Lett.

The Effect of Positivity Constraints on Polarized Parton Densities

The impact of positivity constraints on the polarized parton densities has been studied. Special attention has been paid to the role of positivity constraints in determining the polarized strange quark and gluon densities, which are not well determined from the present data on inclusive polarized DIS.Comment: To appear in the Proceedings of 13th International Workshop on Deep Inelastic Scattering, April, 27 - May, 1, 2005, Madison, Wisconsin, USA, 4 pages, 3 figure

Some Remarks on Methods of QCD Analysis of Polarized DIS Data

The results on polarized parton densities (PDFs) obtained using different methods of QCD analysis of the present polarized DIS data are discussed. Their dependence on the method used in the analysis, accounting or not for the kinematic and dynamic 1/Q^2 corrections to spin structure function g_1, is demonstrated. It is pointed out that the precise data in the preasymptotic region require a more careful matching of the QCD predictions to the data in this region in order to determine the polarized PDFs correctly.Comment: 14 pages, 8 figure

Determination of Polarized PDFs from a QCD Analysis of Inclusive and Semi-inclusive Deep Inelastic Scattering Data

A new combined next to leading order QCD analysis of the polarized inclusive and semi-inclusive deep inelastic lepton-hadron scattering (DIS) data is presented. In contrast to previous combined analyses, the $1/Q^2$ terms (kinematic - target mass corrections, and dynamic - higher twist corrections) in the expression for the nucleon spin structure function $g_1$ are taken into account. The new COMPASS data are included in the analysis. The impact of the semi-inclusive data on the polarized parton densities (PDFs) and on the higher twist corrections is discussed. The new results for the PDFs are compared to our (Leader, Sidorov, Stamenov) LSS'06 PDFs, obtained from the fit to the inclusive DIS data alone, and to those obtained from the de Florian, Sassot, Stratmann, and Vogelsang global analysis.Comment: 11 pages, 8 figures, a version to be published in Phys. Rev.

A New Study of the Polarized Parton Densities in the Nucleon

We present a new next-to-leading order QCD analysis of the world data on inclusive polarized deep inelastic lepton-nucleon scattering adding to the old set of data the final SMC results, the HERMES proton and very recent SLAC/E155 deuteron data. We find an excellent fit to the data and present results for the polarized parton densities in different factorization schemes. These results are in a good agreement with what follows from the theory. We have also found that the main effect of the newly incorporated data is a better determination of the polarized gluon density.Comment: 9 pages, latex, 5 ps figures Presented at the 7th International Workshop on Deep Inelastic Scattering and QCD, Zeuthen, Germany, April 19-23, 199

Scheme Dependence in Polarized Deep Inelastic Scattering

We study the effect of scheme dependence upon the NLO QCD analysis of the world data on polarized DIS. The reliability of an analysis at NLO is demonstrated by the consistency of our polarized densities with the NLO transformation rules relating them to each other. We stress the importance of the chiral JET scheme in which all the hard effects are consistently absorbed in the Wilson coefficient functions.Comment: 11 pages, LaTeX, 3 figures appended as 3 separate ps files. Paper submitted to Phys. Lett.