Beam-Spin Asymmetries in the Azimuthal Distribution of Pion Electroproduction

TL;DR

This paper reports measurements of beam-spin asymmetries in pion electroproduction, revealing how asymmetry amplitudes vary with kinematic variables, and compares these results to theoretical models.

Contribution

It provides the first detailed measurement of beam-spin asymmetries in semi-inclusive pion electroproduction at HERMES, offering new data for testing theoretical models.

Findings

Asymmetry amplitudes depend on Bjorken x, pion energy, and transverse momentum.

Results show sinusoidal dependence on azimuthal angle φ.

Data agree with some theoretical predictions, constraining models.

Abstract

A measurement of the beam-spin asymmetry in the azimuthal distribution of pions produced in semi-inclusive deep-inelastic scattering off protons is presented. The measurement was performed using the {HERMES} spectrometer with a hydrogen gas target and the longitudinally polarized 27.6 GeV positron beam of HERA. The sinusoidal amplitude of the dependence of the asymmetry on the angle $\phi$ of the hadron production plane around the virtual photon direction relative to the lepton scattering plane was measured for $\pi^+,\pi^-$ and $\pi^0$ mesons. The dependence of this amplitude on the Bjorken scaling variable and on the pion fractional energy and transverse momentum is presented. The results are compared to theoretical model calculations.