Flavor Decomposition of the Polarized Quark Distributions in the Nucleon from Inclusive and Semi-inclusive Deep-inelastic Scattering

TL;DR

This paper measures spin asymmetries in deep-inelastic scattering to extract polarized quark distributions, revealing flavor-specific polarization patterns and testing fundamental sum rules and theoretical models.

Contribution

It provides the first detailed flavor decomposition of polarized quark distributions using semi-inclusive data, comparing results with theoretical predictions and sum rules.

Findings

Up quark polarization is positive.

Down quark polarization is negative.

Sea quark polarization is compatible with zero.

Abstract

Spin asymmetries of semi-inclusive cross sections for the production of positively and negatively charged hadrons have been measured in deep-inelastic scattering of polarized positrons on polarized hydrogen and 3He targets, in the kinematic range 0.023<x<0.6 and 1 GeV^2<Q^2<10 GeV^2. Polarized quark distributions are extracted as a function of x for up $(u+u_bar) and down (d+d_bar) flavors. The up quark polarization is positive and the down quark polarization is negative in the measured range. The polarization of the sea is compatible with zero. The first moments of the polarized quark distributions are presented. The isospin non-singlet combination Delta_q_3 is consistent with the prediction based on the Bjorken sum rule. The moments of the polarized quark distributions are compared to predictions based on SU(3)_f flavor symmetry and to a prediction from lattice QCD.