Dimiter B. Stamenov

Determination of polarized parton densities 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 g1 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.

Longitudinal polarized parton densities updated

We have reanalyzed the world data on inclusive polarized DIS, in both NLO and LO QCD, including the new HERMES and COMPASS data. The updated NLO polarized densities are given in both the

Impact of CLAS and COMPASS data on polarized parton densities and higher twist

\overline{\mathrm{MS}}

A new evaluation of polarized parton densities in the nucleon

and JET schemes. The impact of the new data on the results is discussed.

NLO QCD ANALYSIS OF POLARIZED DEEP INELASTIC SCATTERING

We have reanalyzed the world data on inclusive polarized deep inelastic scattering (DIS) including the very precise CLAS proton and deuteron data, as well as the latest COMPASS data on the asymmetry A{sub 1}{sup d}, and have studied the impact of these data on polarized parton densities and higher twist effects. We demonstrate that the low Q{sup 2} CLAS data improve essentially our knowledge of higher twist corrections to the spin structure function g{sub 1}, while the large Q{sup 2} COMPASS data influence mainly the strange quark density. In our new analysis we find that a negative polarized gluon density, or one that changes sign as a function of x, cannot be ruled out on the basis of the present DIS data.

A new study of the polarized parton densities in the nucleon

Abstract. We present a new leading and next-to-leading QCD analysis of the world data on inclusive polarized deep inelastic scattering. A new set of polarized parton densities is extracted from the data and the sensitivity of the results to the newly incorporated SLAC/E155 proton data is discussed.

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

We have carried out a next-to-leading order QCD analysis of the experimental data on polarized DIS in the

SCHEME DEPENDENCE IN POLARIZED DEEP INELASTIC SCATTERING

\overline{\rm MS}

A Possible Resolution of the Strange Quark Polarization Puzzle

scheme. We have studied two models of the parametrizations of the input parton densities — the first due to Brodsky, Burkhardt and Schmidt (BBS), which gives a simultaneous parametrization for the polarized and unpolarized densities and in which the counting rules are strictly imposed; in the second, the input polarized densities are written in terms of the unpolarized ones in the generic form Δq(x)=f(x)q(x), with f(x) some simple smooth function. In both cases a good fit to the polarized data is achieved. As expected, the polarized data do not allow a precise determination of the polarized gluon density. Concerning the polarized sea quark densities, these are fairly well determined in the BBS model because of the interplay of polarized and unpolarized data, whereas in the second model, where only the polarized data are relevant, the polarized sea quark densities are largely undete...

Role of higher twist in polarized deep inelastic scattering

Abstract 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.