Recent results on the helicity structure of the nucleon from HERMES

TL;DR

The HERMES experiment measured spin asymmetries in deep-inelastic scattering to extract the nucleon's helicity structure, quark polarizations, and test flavor symmetry in the polarized sea, providing high-precision data and first measurements of sea quark asymmetry.

Contribution

This work provides the first measurement of flavor asymmetry in the polarized light sea and high-precision extraction of the nucleon's helicity structure from semi-inclusive data.

Findings

Polarized structure function g_1^d measured with high precision.

Quark polarizations for u, ubar, d, dbar, and s+sbar extracted.

No significant flavor asymmetry found in the polarized light sea.

Abstract

The HERMES experiment has measured double spin asymmetries of inclusive and semi-inclusive cross sections for the production of charged hadrons in deep-inelastic scattering of polarised positrons on polarised hydrogen and deuterium targets, in the kinematic range 0.023 < x < 0.6, and 1 GeV^2 < Q^2 < 15 GeV^2. For the data taken on the deuterium target, a RICH detector provides the complete identification of charged pions and kaons. From the inclusive measurements on deuterium, the polarised structure function g_1^d has been extracted with high precision. Together with the semi-inclusive measurements, quark polarisations are extracted separately for the u, ubar, d, dbar, and (s + sbar) flavours in a LO QCD analysis. Furthermore, a possible breaking of flavour symmetry in the polarised light sea, (Delta ubar - Delta dbar), was measured for the first time and found to be consistent with zero within the experimental precision.