Beam-spin asymmetries from semi-inclusive pion electroproduction

Abstract

We have measured the moment ${A}_{LU}^{\mathrm{sin}\ensuremath{\phi}}$ corresponding to the polarized electron beam-spin asymmetry in semi-inclusive deep inelastic scattering. ${A}_{LU}^{\mathrm{sin}\ensuremath{\phi}}$ is a twist-3 quantity providing information about quark-gluon correlations. Data were taken with the CLAS Spectrometer at Jefferson Lab using a 5.498 GeV longitudinally polarized electron beam and an unpolarized liquid hydrogen target. All three pion channels (${\ensuremath{\pi}}^{+}$, ${\ensuremath{\pi}}^{0}$ and ${\ensuremath{\pi}}^{\ensuremath{-}}$) were measured simultaneously over a large range of kinematics within the virtuality range ${Q}^{2}\ensuremath{\approx}\text{ }1.0--4.5\text{ }\text{ }{\mathrm{GeV}}^{2}$. The observable was measured with better than 1% statistical precision over a large range of $z$, ${P}_{T}$, ${x}_{B}$, and ${Q}^{2}$, which permits comparison with several reaction models. The discussed measurements provide an upgrade in statistics over previous measurements, and serve as the first evidence for the negative sign of the ${\ensuremath{\pi}}^{\ensuremath{-}}$ $\mathrm{sin}\ensuremath{\phi}$ moment.