Double spin asymmetry AL̳T̳ in charged pion production from deep inelastic scattering on a transversely polarized ³He target

Abstract

In this thesis I discuss the first measurement of the beam-target double-spin asymmetry ALT for charged pion electroproduction in deep inelastic electron scattering on a transversely polarized 3He target. These data were taken between October 2008 to February 2009 using a 5.9 GeV polarized electron beam at Thomas Jefferson National Accelerator Facility Experimental Hall A. The kinematics focused on the valence quark region, 0.16 < x < 0.35 with 1.4 < Q2 < 2.7 GeV2. The systematic uncertainties in this measurement due to acceptance, detector response drift, target density fluctuations and single spin asymmetries were suppressed to a negligible level by the frequent reversals of both beam helicity and target spin direction. Using the effective polarization approximation, the neutron ALT asymmetries were extracted from the measured 3He asymmetries and proton over 3He cross section ratios. The ALT asymmetries probe the poorly known transverse momentum dependent parton distribution function gq/1T, which describes the longitudinal polarization of quarks in a transversely polarized nucleon. The gq/1T function requires an interference between wave function components differing by one unit of quark OAM, and therefore provide access to quark spin-orbit correlations in the nucleons. While the measured [pi]+ asymmetries are consistent with zero, these data indicate a positive azimuthal asymmetry for [pi]- production on 3He and the neutron, which at leading twist leads to a non-zero gq/1T. This work has laid the foundation for the future high precision mapping of the ALT asymmetries, which is also discussed in this thesis.