We report the first evidence for a nonzero beam-spin azimuthal asymmetry in the electroproduction of positive pions in the deep-inelastic kinematic region. Data for the reaction ep→e′ π+X have been obtained using a polarized electron beam of 4.3 GeV with the CEBAF Large Acceptance Spectrometer at the Thomas Jefferson National Accelerator Facility. The amplitude of the sin φ modulation increases with the momentum of the pion relative to the virtual photon, z. In the range z=0.5-0.8 the average amplitude is 0.038±0.005 ±0.003 for a missing mass Mx> 1.1 GeV and 0.037±0.007±0.004 for Mx> 1.4 GeV.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)