200920092006-11-03/2009-11-03University of Illinois, Diss., 2009; 121 pp., (2009). doi:10.3204/DESY-THESIS-2009-045The motivation for this work was to improve upon prior analyses that extracted the quark helicity distributions, ¢q(x), of the proton. These extractions, performed by the HERMES collaboration, were excellent analyses, the most recent of which contained the vast majority of the data analyzed here. \If they were so good, how much could you improve on their results?' one might ask. Well, not to spoil the punch line, but some. The precision was improved modestly and our understanding of the systematic uncertainties was improved more signi¯cantly. The reader is welcome to jump to Chapter 6 and see. The approach that we took however was to try many new things. Not all of these e®orts yielded improvements on the scale we had hoped for, but many interesting new techniques were developed and we were able to produce several related new results along the way. Let me suggest then that rather than thinking of Chapter 6 as the result of this analysis, consider that there are valuable new results and insights scattered throughout this work. Chapter 4 contains several new double-spin asymmetries which are results in their own right. The ph? dependence is plotted for the ¯rst time with HERMES data which is uniquely hadron separated. The hadron charge di®erence asymmetry is presented which, in combination with the quark helicity densities of Chapter 6, can put limits on fragmentation symmetry breaking in semi-inclusive DIS. Additionally, a novel method of unfolding yields (reducing smearing e®ects from detector resolution limitations and QED radiation) was developed and presented here for the ¯rst time which potentially allows new kinds of asymmetries to be constructed which were unavailable before. Also, this chapter describes the method by which the ¯rst ever three dimensionally binned SIDIS double-spin asymmetries were produced. These asymmetries, which will be used as the data inputs for the ¢q(x) extraction, are valuable inputs to world ¯ts being performed by theorists. Chapter 5 further explores this idea of fragmentation symmetry breaking with Monte Carlo studies of fragmentation functions. These studies test assumptions which are frequently made in the interpretation of asymmetries like the hadron charge di®erence of the prior chapter and suggest that these assumptions should be approached with some caution. Also, a technique for tuning and more importantly propagating systematic uncertainty through non-analytic Monte Carlo models, like the Lund-String model which provides an essential input to the ¢q(x) extraction, is developed vi and potentially has widespread applications. That being said, the author hopes you enjoy the techniques developed and results presented in the following chapters.Published by Deutsches Elektronen-Synchrotron, DESY, Hamburg10.3204/DESY-THESIS-2009-045eng2009Deutsches Elektronen-Synchrotron, DESY, HamburgDissertationpages 121thesiselectron p: semi-inclusive reactionelectron deuteron: semi-inclusive reactionpolarized beam: longitudinalpolarized target: longitudinalhadron: electroproductionspin: asymmetrynucleon: polarizabilityfragmentation: modelhadron: multiplicityquark: helicityparton: distribution functiondata analysis methodHERMESDESY HERA Stor27.6 GeVPolarization, motion, and fragmentation: Exploring the role of quarks in the nucleon through semi-inclusive longitudinal spin asymmetries at HERMESRubin, Joshua George