Single-spin azimuthal asymmetry in exclusive electroproduction of pi+ mesons on transversely polarized protons

TL;DR

This study measures the single-spin azimuthal asymmetry in exclusive pi+ meson electroproduction on transversely polarized protons, revealing mostly null results except for one significant interference term involving photon polarization states.

Contribution

It provides the first detailed measurement of azimuthal asymmetries in exclusive pi+ production on polarized protons, highlighting the role of interference between photon polarization contributions.

Findings

Fourier components of asymmetry are mostly zero.

One large asymmetry component involving photon interference was observed.

Results suggest specific interference effects in the production process.

Abstract

Exclusive electroproduction of pi+ mesons was studied by scattering 27.6 GeV positrons or electrons off a transversely polarized hydrogen target. The single-spin azimuthal asymmetry with respect to target polarization was measured as a function of the Mandelstam variable t, the Bjorken scaling variable x_B, and the virtuality Q^2 of the exchanged photon. The extracted Fourier components of the asymmetry were found to be consistent with zero, except one that was found to be large and that involves interference of contributions from longitudinal and transverse virtual photons.