Hermes and the spin of the proton

TL;DR

The HERMES experiment investigates the spin structure of the nucleon through various semi-inclusive scattering measurements, providing insights into polarized quark distributions, gluon polarization, and nucleon tensor spin.

Contribution

This paper presents new experimental data on spin asymmetries and azimuthal asymmetries, offering novel insights into the flavor decomposition and gluon polarization in the nucleon.

Findings

Data on semi-inclusive pion, kaon, and proton asymmetries

First glimpse of gluon polarization

Observation of azimuthal asymmetries related to nucleon spin

Abstract

HERMES is a second generation experiment to study the spin structure of the nucleon, in which measurements of the spin dependent properties of semi-inclusive deep-inelastic lepton scattering are emphasized. Data have been accumulated for semi-inclusive pion, kaon, and proton double-spin asymmetries, as well as for high-p_T hadron pairs, and single-spin azimuthal asymmetries for pion electroproduction and deep virtual Compton scattering. These results provide information on the flavor decomposition of the polarized quark distributions in the nucleon and a first glimpse of the gluon polarization, while the observation of the azimuthal asymmetries show promise for probing the tensor spin of the nucleon and isolating the total angular momentum carried by the quarks.