Polarization, motion, and fragmentation: Exploring the role of quarks in the nucleon through semi-inclusive longitudinal spin asymmetries at HERMES.

摘要

This dissertation presents an analysis of deep inelastic scattering data, with polarized electron beam and polarized hydrogen and deuterium gas targets, taken by the HERMES collaboration at the DESY laboratory in Hamburg, Germany. Double-spin Born asymmetries are presented. Semi-inclusive (hadron-identified) asymmetries are binned in the parton momentum fraction (Bjorken-x), hadron energy fraction, z, and transverse momentum. Kinematic dependences of these asymmetries are explored. A leading order purity extraction of the quark polarizations and helicity densities is performed using these three-dimensionally binned semi-inclusive asymmetries and purities matrices generated with a Lund-String fragmentation Monte-Carlo simulation. Additionally, a new rigorous procedure for tuning this phenomenological model and estimating its contribution to the systematic uncertainty of the quark polarizations is included. Other subjects explored are the influence of the target remnant on often trusted fragmentation symmetry assumptions and an improved procedure for correcting the smearing effects of limited detector resolution and QED radiation.