Single-spin asymmetries in semi-inclusive pion production

TL;DR

This paper reports the first measurement of single-spin asymmetries in semi-inclusive pion production using a transversely polarized hydrogen target, providing insights into quark distribution functions relevant for understanding nucleon spin structure.

Contribution

It introduces the first measurement of single-spin asymmetries in semi-inclusive pion production with a transversely polarized target, relating asymmetries to transversity and Sivers functions.

Findings

Two sine-modulations related to quark distributions were extracted.

The asymmetries include small sub-leading twist contributions.

Results complement previous measurements with different target polarizations.

Abstract

For the first time single-spin asymmetries in semi-inclusive pion production are measured by the HERMES experiment with a transversely polarised hydrogen target. Two different sine-modulations are extracted which can be related to the transversity \delta q(x) and Sivers f_{1T}^{\perp q}(x) quark distribution functions. The extracted sine-moments still contain small sub-leading twist contributions which can be extracted from HERMES data combining the results from the transversely polarised hydrogen target with previously measured results from a longitudinally polarised hydrogen target.