[en] This document describes the recent experimental results on the spin structure of the nucleon obtained with the electron accelerator Thomas Jefferson National Facility (Jefferson Lab), Virginia. We first discuss the goal of studying the nucleon spin structure and give the basis and phenomenology of high energy lepton scattering. Then, we discuss with some details a few sum rules concerning the spin structure of the nucleon. Those are important tools for studying the nucleon spin structure at Jefferson Lab. We then describe the present experimental situation and analyze the results. We have been able to determine an effective coupling constant for the strong interaction for any regime of quantum chromodynamics which proves that QCD is an approximately conformal theory. We conclude on the perspectives for this field of research, in particular with the 12 GeV energy upgrade of Jefferson Lab. The top priority will be the measurement of generalised parton distributions. The only issue that will stay misunderstood is the role of the very low x domain on the spin structure of the nucleon

[en] This thesis presents an experimental study of the neutron (and ³He) spin structure with a particular emphasis in the resonance domain (experiment E94010 that took place in 1997 at Jefferson Lab (TJNAF or formerly CEBAF) in Virginia). A polarized ³He target was built in order to achieve this study since polarized ³He nuclei can be seen as polarized neutrons. This target allowed the measurement of the polarized absolute cross sections σ_1/2(Q², ν) and σ_3/2(Q², ν) from the inclusive reaction ^→3He(^→e, e')X for incident beam energies ranging from 0.86 GeV to 5.07 GeV at a scattering angle of 15.5 deg. The Q² evolution of the generalized Gerasimov-Drell-Hearn (GDH) integral on ³He and on neutron was measured from 0.1 GeV² to 1.0 GeV² in order to understand the transition between perturbative QCD and non-perturbative QCD. The integration domain in ν (the energy loss of the scattered electron) is from the pion threshold to about 2.5 GeV which covers both the resonance region and the Deep Inelastic Scattering. The high precision of our data constrains the models giving the Q² evolution of the generalized GDH integral. The polarized quasi-elastic scattering was also measured. The cross section σ^TT(Q², ν) on ³He and the spin structure functions g₁^3He(Q², ν) and g₂^3He(Q², ν) are presented. These data are an indication that the higher-twists are small in our kinematics domain and that the Bloom-Gilman duality seems to hold for the polarized spin structure functions. (author)

[en] We present recent results from Jefferson Lab on sum rules related to the spin structure of the nucleon. We then discuss how the Bjorken sum rule with its connection to the Gerasimov-Drell-Hearn sum, allows us to conveniently define an effective coupling for the strong force at all distances. (author)

[en] The Jefferson Lab Hall A polarized ³He (neutron spin structure) program is presented with a special focus on the measurement of the Q² evolution of the generalized GDH integral. (author)

[en] We report on the measurement of the Bjorken sum in the range 0.16< Q²<1.1 GeV². The extraction of an effective strong coupling constant is then discussed

[en] The Gerasimov-Drell-Hearn sum rule, which was originally derived at Q² 0, has been extended recently to finite Q². The measurement of its Q² behavior provides a powerful way to investigate the transition between the partonic and hadronic description of QCD. I recall first the theoretical grounds of GDH. Then new experimental results on both the original and extended sum rules are discussed. Here, I focus on the results obtained in Hall A at Jefferson Lab. I will conclude by presenting the experimental perspectives, both at low Q² and at large photon energies. (author)

[en] In this work, we present the results of our final analysis of the full data set of g^p₁ (Q²), the spin structure function of the proton, collected using CLAS at Jefferson Laboratory in 2000–2001. Polarized electrons with energies of 1.6, 2.5, 4.2, and 5.7 GeV were scattered from proton targets (¹⁵NH₃ dynamically polarized along the beam direction) and detected with CLAS. From the measured double spin asymmetries, we extracted virtual photon asymmetries A^p₁ and A^p₂ and spin structure functions g^p₁ and g^p₂ over a wide kinematic range (0.05 GeV² < Q² < 5 GeV² and 1.08 GeV < W < 3 GeV) and calculated moments of g^p₁. We compare our final results with various theoretical models and expectations, as well as with parametrizations of the world data. Lastly, our data, with their precision and dense kinematic coverage, are able to constrain fits of polarized parton distributions, test pQCD predictions for quark polarizations at large x, offer a better understanding of quark-hadron duality, and provide more precise values of higher twist matrix elements in the framework of the operator product expansion.

[en] In this paper we discuss effective strong coupling constants. Those are well behaved in the low-Q² domain, contrarily to α_s from perturbative Quantum Chromodynamics (pQCD). We present an extraction of an effective strong coupling constant from Jefferson Lab polarized data at intermediate and low Q². We also show how these data, together with spin sum rules, allow us to obtain the effective coupling constant over the entire Q² range. We then discuss the relation between the experimentally extracted coupling constant and theoretical calculations at low Q². We conclude on the importance of such study for the application of the Anti-de-Sitter space/Conformal Field Theory (AdS/CFT) correspondence to QCD.

[en] We present recent results on the Bjorken and the generalized forward spin polarizability sum rules from Jefferson Lab Hall A and CLAS experiments, focusing on the low Q² part of the measurements. We then discuss the comparison of these results with Chiral Perturbation theory calculations. In the second part of this paper, we show how the Bjorken sum rule with its connection to the Gerasimov-Drell-Hearn sum, allows us to conveniently define an effective coupling for the strong force at all distances.

[en] We present the recent JLab measurements on moments of spin structure functions at intermediate and low Q2. The Bjorken sum and Burkhardt-Cottingham sum on the neutron are presented. The later appears to hold. Higher moments (generalized spin polarizabilities and d₂ⁿ) are shown and compared to chiral perturbation theory and lattice QCD respectively