Single-spin azimuthal asymmetry in exclusive electroproduction of pi^+ mesons

TL;DR

This paper reports the first measurement of single-spin azimuthal asymmetry in exclusive pi^+ meson electroproduction, revealing its dependence on kinematic variables and providing insights into nucleon structure.

Contribution

It presents the first measurement of the sin φ polarization asymmetry in exclusive pi^+ electroproduction off polarized protons, expanding understanding of spin effects in deep-inelastic scattering.

Findings

Asymmetry magnitude grows with decreasing x

Asymmetry increases with increasing -t

Asymmetry vanishes at t -> t_min

Abstract

A single-spin asymmetry in the distribution of exclusively produced pi^+ mesons azimuthally around the virtual photon direction relative to the lepton scattering plane has been measured for the first time in deep-inelastic scattering of positrons off longitudinally polarized protons. Integrated over the experimental acceptance, the sin \phi moment of the polarization asymmetry of the cross section is measured to be -0.18 +/- 0.05 (stat.) +/- 0.02 (syst.). The asymmetry is also studied as a function of the relevant kinematic variables, and its magnitude is found to grow with decreasing x and increasing -t and vanish at t -> t_min (where x is the Bjorken scaling variable and t is the squared four-momentum transferred to the nucleon).