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

TL;DR

This work presents a comprehensive NLO QCD analysis of polarized inclusive and semi-inclusive DIS data, incorporating target mass corrections and higher-twist terms in g1 and integrating COMPASS measurements. The methodology combines a flexible polarized PDF parameterization with SU(2) and SU(3) sum rules and uses a double Mellin transform to compute SIDIS observables with fragmentation functions. A key outcome is that SIDIS enables flavor separation of sea quarks, revealing nuanced behavior for Δubar, Δbar{d}, and Δbar{s}, while the polarized gluon density ΔG remains ambiguous under current data and FF choices. The study also confirms non-negligible higher-twist effects in the preasymptotic region and underscores the ongoing challenge of fully resolving the proton spin budget, including orbital angular momentum, with present data and FF uncertainties.

Abstract

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.

Figures (8)

• Figure 1: Comparison of our NLO QCD results for the SIDIS asymmetries with the data at measured $x$ and $Q^2$.
• Figure 2: Our NLO sea quarks and gluon polarized PDFs at $Q^2=2.5~GeV^2$ in the $\rm \overline{MS}$ scheme. For comparison the DSSV PDFs DSSV are also presented.
• Figure 3: Our results for $\Delta u$, $\Delta d$, $(\Delta u+\Delta \bar{u})$ and $(\Delta d+\Delta \bar{d})$ polarized parton densities at NLO approximation. DSSV DSSV as well as LSS'06 LSS07 results for the corresponding densities are presented too.
• Figure 4: Comparison between HT values corresponding to the fits of inclusive DIS LSS07 and combined inclusive and SIDIS data set (this analysis).
• Figure 5: Comparison between the positive and sign-changing gluon densities. The corresponding error bands are also shown.