One of the main approaches toward understanding the hadronic structure is the introduction of transverse momentum dependent parton distribution functions (TMDs). These non-perturbative objects are accessible through deeply inelastic processes such as semi-inclusive deep inelastic scattering (SIDIS), Drell-Yan and e+e- annihilation. The current thesis explores the hadronic structure within the TMD approach under three independent chapters. As the first study in the present thesis the complete cross-section for the production of unpolarized hadrons in e-p semi-inclusive deep-inelastic scattering is computed up to power-suppressed O(1=Q2) terms, utilizing an approximation which systematically assumes that ̄qgq-terms are much smaller than ̄qq-correlators. All leading- and subleading-twist structure functions are calculated in terms of six TMDs and two fragmentation functions for which phenomenological extractions are available. The results are compared to available experimental data from COMPASS, HERMES and Jeerson Lab. p Drell-Yan process is the subject of the second study in this thesis. All leading-twist structure functions of -induced Drell-Yan with polarized protons are computed at the scale of COMPASS experiment. The non-perturbative inputs for the TMDs are taken from available phenomenological extractions plus two well-established models: The light-front constituent quark model and the spectator model. Evolution eects are estimated using a Gaussian ansatz with energy-dependent Gaussian widths. The results are compared to COMPASS data when available leading to important conclusions about pion and proton TMDs. Predictions are made for future experiments. The third study in this thesis aims at establishing a generalized covariant parton model that allows us to obtain all possible TMDs in a systematic way by describing the quark correlator in terms of two covariant distribution functions for on-shell partons. The proposed formulation of the model successfully reproduces all results of the original version of the model for the leading-twist time-reversal-even (T-even) TMDs and enables us to evaluate all T-even twist-3 TMDs for the first time. The unpolarized and helicity parton distribution functions are used as inputs and other TMDs are calculated then compared to available TMD parametrizations. The results show several model relations between the TMDs some of which are expected from QCD and some verified in other quark models as well.

In this talk, we will present a QCD factorization theorem for the semi-inclusive deep-inelastic scattering with hadrons in the current fragmentation region detected at low transverse momentum. There has been considerable experimental and theoretical interest in semi-inclusive hadron production in deep inelastic scattering (SIDIS) processes. For example, by studying the polarized and unpolarized SIDIS, one will be able to identify the sea quark distribution and polarization in nucleon, and the experimental results from the HERMES collaboration have revealed nontrivial sea structure in nucleon [1]. More recently, SIDIS opened a new window to study the transverse momentum dependent (TMD) parton distributions and fragmentation functions from the low transverse momentum hadron production. The transverse momentum distribution of the final state hadron is directly related to the transverse momentum dependence of the parton distributions and fragmentation. These studies will provide new opportunities to explore the partonic structure of nucleon, especially the three-dimension distribution of partons inside nucleon. The DIS experiments, including HERMES, COMPAS, and JLab Hall B collaborations, have studied various azimuthal asymmetries in SIDIS. In particular, the HERMES collaboration found sizable single spin asymmetries in these processes involving nontrivial QCD effects and hadron structure.

Straddling the traditional disciplines of nuclear and particle physics, hadron physics is a vital and extremely active research area, as evidenced by a 2004 Nobel prize and new research facilities, such as that scheduled to open at CERN. Scientifically it is of vital importance in extrapolating our knowledge of quark-gluon physics at the sub-nucleo

Giving an accurate account of the concepts, theorems and their justification, this book is a systematic treatment of perturbative QCD. It relates the concepts to experimental data, giving strong motivations for the methods. Ideal for graduate students starting their work in high-energy physics, it will also interest experienced researchers.

Almost all of the visible matter in the universe is built from strongly interacting particles known as hadrons. For example, protons and neutrons, which comprise the nucleus of an atom, fit into this class of particles. However, hadrons are not a fundamental form of matter in that they are composed of other particles collectively called partons. One of the main challenges we face is to understand this internal structure. In the past, focus was placed mainly on reactions that involved so-called collinear twist-2 two-parton correlators. Even though these functions provide valuable access to the interior of hadrons, they present us with only a 1-dimensional and, hence, incomplete view of this complex world. In recent years, two extensions of this formalism have become an active source of research: transverse momentum dependent (TMD) functions and three-parton correlations. The former allow us to obtain a 3-dimensional image of hadrons (in momentum space), while the latter give us insight into the rich interactions that occur inside of them, and the two are closely connected. In this dissertation we analyze spin asymmetries in hard scattering processes, which address both types of functions, in order to understand the parton dynamics that cause these phenomena and to determine what these observables reveal about the inner-workings of hadrons. Namely, we analyze (almost back-to-back) di-hadron production in electron-positron annihilation as well as discuss momentum sum rules for some of the associated TMD functions. We also investigate transverse single-spin asymmetries in lepton-nucleon and proton-proton collisions. The study of the former allows us to comment on the general role of parton re-scattering in such effects, while a discussion of the latter includes a new computation of an important piece to that observable. Furthermore, we present pioneering calculations on longitudinal-transverse double-spin asymmetries in nucleon-nucleon collisions.

This thesis examines the γZ box contribution to the weak charge of the proton. Here, by combining recent parity-violating electron-deuteron scattering data with our current understanding of parton distribution functions, the author shows that one can limit this model dependence. The resulting construction is a robust model of the γγ and γZ structure functions that can also be used to study a variety of low-energy phenomena. Two such cases are discussed in this work, namely, the nucleon’s electromagnetic polarizabilities and quark-hadron duality. By using phenomenological information to constrain the input structure functions, this important but previously poorly understood radiative correction is determined at the kinematics of the parity-violating experiment, QWEAK, to a degree of precision more than twice that of the previous best estimate. A detailed investigation into available parametrizations of the electromagnetic and interference cross-sections indicates that earlier analyses suffered from the inability to correctly quantify their model dependence.

The fully unintegrated, off-diagonal quark-quark correlator for a spin-1/2 hadron is parameterized in terms of so-called generalized parton correlation functions. Such objects, in particular, can be considered as mother distributions of generalized parton distributions on the one hand and transverse momentum dependent parton distributions on the other. Therefore, our study provides new, model-independent insights into the recently proposed nontrivial relations between generalized and transverse momentum dependent parton distributions. We find that none of these relations can be promoted to a model-independent status. As a by-product we obtain the first complete classification of generalized parton distributions beyond leading twist. The present paper is a natural extension of our previous corresponding analysis for spin-0 hadrons.

In this paper we present a comprehensive formalism for dilepton production from the collision of two polarized spin-1/2 hadrons by identifying the general angular distribution of the cross section in combination with a complete set of structure functions. The various structure functions are computed in the parton model approximation where we mainly consider the case when the transverse momentum of the dilepton pair is much smaller than its invariant mass. In this kinematical region dilepton production can be described in terms of transverse momentum dependent parton distributions.

Analyzes the theoretical questions related to electron and photon interactions at high energies.