Valence and sea contributions to the nucleon spin

TL;DR

This paper directly extracts the valence quark contributions to the proton spin from polarized SIDIS data without fitting, and finds sea quark contributions are consistent with zero, providing insights into nucleon spin structure.

Contribution

It presents a novel direct extraction method for valence PDFs in NLO QCD from experimental data, avoiding fitting procedures and estimating sea quark contributions.

Findings

Valence quark contributions are significant and well-determined.

Sea quark contributions are compatible with zero within errors.

Method provides a new way to analyze nucleon spin structure.

Abstract

The first moments of the polarized valence parton distribution functions (PDFs) truncated to the wide Bjorken $x$ region $0.004<x<0.7$ are directly (without any fitting procedure) extracted in the next to leading order (NLO) QCD from both COMPASS and HERMES data on pion production in polarized semi-inclusive DIS (SIDIS) experiments. The COMPASS and HERMES data are combined in two ways and two scenarios for the fragmentation functions (FFs) are considered. Two procedures are proposed for an estimation of light sea quark contributions to the proton spin. Both of them lead to the conclusion that these contributions are compatible with zero within the errors.