Higher Twist Effects in Polarized DIS

The size of higher twist corrections to the spin proton and neutron g1 structure functions and their role in determining the polarized parton densities in the nucleon is discussed.Comment: 6 pages, 2 figures, to appear in the proceedings of First Workshop on Quark-Hadron Duality and the Transition to pQCD, Frascati, June 6-8, 200

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

Determination of the fragmentation functions from an NLO QCD analysis of the HERMES data on pion multiplicities

An NLO QCD analysis of the final HERMES data on pion multiplicities is presented and a new set of pion fragmentation functions is extracted from the best fit to the data. We have studied the so-called [x,z] and [Q^2,z] presentations of their data, as given by HERMES, which, in principle, should simply be two different ways of presenting the experimental data. We have based our extraction on an excellent fit to the [Q^2,z] presentation of the data. We also draw attention to what appears to be a problem with the [x,z] presentation of the HERMES data.Comment: 12 pages, 7 figures; This updated version corresponds to the paper accepted for publication in Phys. Rev.

New analysis concerning the strange quark polarization puzzle

The fact that analyses of semi-inclusive deep inelastic scattering suggest that the polarized strange quark density $\Delta s(x) + \Delta \bar{s}(x)$ is positive in the measured region of Bjorken x, whereas all analyses of inclusive deep inelastic scattering yield significantly negative values of this quantity, is known as the "strange quark polarization puzzle". We have analyzed the world data on inclusive deep inelastic scattering, including the COMPASS 2010 proton data on the spin asymmetries, and for the first time, the new extremely precise JLab CLAS data on the proton and deuteron spin structure functions. Despite allowing in our parametrization, for a possible sign change, our results confirm that the inclusive data yield significantly negative values for the polarized strange quark density.Comment: 8 pages, 3 figures, 3 tables; misprints for the values of $\chi^2/DOF$ in page 5 correcte

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