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

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

On Combining High and Low Q**2 Information on the Polarized Parton Densities

We draw attention to some problems in the combined use of high-Q^2 deep inelastic scattering (DIS) data and low-Q^2 hyperon \beta-decay data in the determination of the polarized parton densities. We explain why factorization schemes like the JET or AB schemes are the simplest in which to study the implications of the DIS parton densities for the physics of the low-Q^2 region.Comment: 10 pages, LaTeX, minor corrections made in Section 4, a reference added, to be published in JHE

On the controversy concerning the definition of quark and gluon angular momentum

A major controversy has arisen in QCD as to how to split the total angular momentum into separate quark and gluon contributions, and as to whether the gluon angular momentum can itself be split, in a gauge invariant way, into a spin and orbital part. Several authors have proposed various answers to these questions and offered a variety of different expressions for the relevant operators. I argue that none of these is acceptable and suggest that the canonical expression for the momentum and angular momentum operators is the correct and physically meaningful one. It is then an inescapable fact that the gluon angular momentum operator cannot, in general, be split in a gauge invariant way into a spin and orbital part. However, the projection of the gluon spin onto its direction of motion i.e. its helicity is gauge invariant and is measured in deep inelastic scattering on nucleons. The Ji sum rule, relating the quark angular momentum to generalized parton distributions, though not based on the canonical operators, is shown to be correct, if interpreted with due care. I also draw attention to several interesting aspects of QED and QCD, which, to the best of my knowledge, are not commented upon in the standard textbooks on Field Theory.Comment: 41 pages; Some incorrect statements have been rectified and a detailed discussion has been added concerning the momentum carried by quarks and the Ji sum rule for the angular momentu

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.

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.

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