Effect of Orbital Angular Momentum on Valence-Quark Helicity Distributions

We study the quark helicity distributions at large x in perturbative QCD, taking into account contributions from the valence Fock states of the nucleon which have nonzero orbital angular momentum. These states are necessary to have a nonzero anomalous magnetic moment. We find that the quark orbital angular momentum contributes a large logarithm to the negative helicity quark distributions in addition to its power behavior, scaling as (1-x)^5\log^2(1-x) in the limit of x\to 1. Our analysis shows that the ratio of the polarized over unpolarized down quark distributions, \Delta d/d, will still approach 1 in this limit. By comparing with the experimental data, we find that this ratio should cross zero at x\approx 0.75.Comment: 10 pages, 3 eps figure

Predictions for Sivers single spin asymmetries in one- and two-hadron electroproduction at CLAS12 and EIC

The study of the Sivers effect, describing correlations between the transverse polarization of the nucleon and its constituent (unpolarized) parton's transverse momentum, has been the topic of a great deal of experimental, phenomenological and theoretical effort in recent years. Semi-inclusive deep inelastic scattering measurements of the corresponding single spin asymmetries (SSA) at the upcoming CLAS12 experiment at JLab and the proposed Electron-Ion Collider will help to pinpoint the flavor structure and the momentum dependence of the Sivers parton distribution function describing this effect. Here we describe a modified version of the $\tt{PYTHIA}$ Monte Carlo event generator that includes the Sivers effect. Then we use it to estimate the size of these SSAs, in the kinematics of these experiments, for both one and two hadron final states of pions and kaons. For this purpose we utilize the existing Sivers parton distribution function (PDF) parametrization extracted from HERMES and COMPASS experiments. Using this modified version of $\tt{PYTHIA}$, we also show that the the leading order approximation commonly used in such extractions may provide significantly underestimated values of Sivers PDFs, as in our Monte Carlo simulations the omitted parton showers and non-DIS processes play an important role in these SSAs, for example in the COMPASS kinematics.Comment: 18 pages, 27 figures. V2: updated to version published in PRD, two references have been added and some minor changes done to the tex

Studies of spin-orbit correlations at JLAB

Studies of single spin asymmetries for pion electroproduction in semi-inclusive deep-inelastic scattering are presented using the polarized \sim6 GeV electrons from at the Thomas Jefferson National Accelerator Facility (JLab) and the Continuous Electron Beam Accelerator Facility (CEBAF) Large Acceptance Spectrometer (CLAS) with the Inner Calorimeter. The cross section versus the azimuthal angle {\phi}_h of the produced neutral pion has a substantial sin {\phi}_h amplitude. The dependence of this amplitude on Bjorken x_B and on the pion transverse momentum is extracted and compared with published data.Comment: proceedings of SPIN2010 conference (September-October 2010, Juelich-Germany

The transverse momentum dependent distribution functions in the bag model

Leading and subleading twist transverse momentum dependent parton distribution functions (TMDs) are studied in a quark model framework provided by the bag model. A complete set of relations among different TMDs is derived, and the question is discussed how model-(in)dependent such relations are. A connection of the pretzelosity distribution and quark orbital angular momentum is derived. Numerical results are presented, and applications for phenomenology discussed. In particular, it is shown that in the valence-x region the bag model supports a Gaussian Ansatz for the transverse momentum dependence of TMDs

Monte Carlo Generators for Studies of the 3D Structure of the Nucleon

Extraction of transverse momentum and space distributions of partons from measurements of spin and azimuthal asymmetries requires development of a self consistent analysis framework, accounting for evolution effects, and allowing control of systematic uncertainties due to variations of input parameters and models. Development of realistic Monte-Carlo generators, accounting for TMD evolution effects, spin-orbit and quark-gluon correlations will be crucial for future studies of quark-gluon dynamics in general and 3D structure of the nucleon in particular

Studies of the 3D structure of the proton at Jlab

In recent years parton distributions, describing longitudinal momentum, helicity and transversity distributions of quarks and gluons, have been generalized to account also for transverse degrees of freedom. Two new sets of more general distributions, Transverse Momentum Distributions (TMDs) and Generalized Parton Distributions (GPDs) were introduced to describe transverse momentum and spatial distributions of partons. Great progress has been made since then in measurements of different Single Spin Asymmetries (SSAs) in semi-inclusive and hard exclusive processes, providing access to TMDs and GPDs, respectively. Studies of TMDs and GPDs are also among the main driving forces of the JLab 12 GeV upgrade project

Spin orbit correlations and the structure of the nucleon

Extensive experimental measurements of spin and azimuthal asymmetries in various processes have stimulated theoretical interest and progress in the studies of the nucleon structure. The interpretation of experimental data in terms of parton distribution functions, generalized to describe transverse momentum and spatial parton distributions, is one of the main remaining challenges of modern nuclear physics. These new parton distribution and fragmentation functions encode the motion and the position of partons and are often referred to as three-dimensional distributions describing the three-dimensional (3D) structure of the nucleon. Understanding of the production mechanism and performing phenomenological studies compatible with factorization theorems using minimal model assumptions are goals of the analysis of the experimental data. HERMES and COMPASS Collaborations and experiments at Jefferson Lab have collected a wealth of polarized and unpolarized Semi-Inclusive Deep Inelastic Scattering (SIDIS) data. These data play a crucial role in current understanding of nucleon spin phenomena as they cover a broad kinematical range. The Jefferson Lab 12 GeV upgrade data on polarized and unpolarized SIDIS will have a remarkably higher precision at large parton fractional momentum $x$ compared to the existing data. We argue that both experimental and phenomenological communities will benefit from the development of a comprehensive extraction framework that will facilitate the extraction of the 3D nucleon structure, help understand various assumptions in extraction and data analysis, help to insure the model independence of the experimental data and validate the extracted functions. In this review we present the latest developments in the field of the spin asymmetries with emphasis on observables beyond the leading twist in SIDIS, indispensable for studies of the complex 3D nucleon structure, and discuss different components involved in precision extraction of the 3D partonic distribution and fragmentation functions.Extensive experimental measurements of spin and azimuthal asymmetries in various processes have stimulated theoretical interest and progress in the studies of the nucleon structure. The interpretation of experimental data in terms of parton distribution functions, generalized to describe transverse momentum and spatial parton distributions, is one of the main remaining challenges of modern nuclear physics. These new parton distribution and fragmentation functions encode the motion and the position of partons and are often referred to as three-dimensional distributions describing the three-dimensional (3D) structure of the nucleon. Understanding of the production mechanism and performing phenomenological studies compatible with factorization theorems using minimal model assumptions are goals of the analysis of the experimental data. HERMES and COMPASS Collaborations and experiments at Jefferson Lab have collected a wealth of polarized and unpolarized Semi-Inclusive Deep Inelastic Scattering (SIDIS) data. These data play a crucial role in current understanding of nucleon spin phenomena as they cover a broad kinematical range. The Jefferson Lab 12 GeV upgrade data on polarized and unpolarized SIDIS will have a remarkably higher precision at large parton fractional momentum $x$ compared to the existing data. We argue that both experimental and phenomenological communities will benefit from the development of a comprehensive extraction framework that will facilitate the extraction of the 3D nucleon structure, help understand various assumptions in extraction and data analysis, help to insure the model independence of the experimental data and validate the extracted functions. In this review we present the latest developments in the field of the spin asymmetries with emphasis on observables beyond the leading twist in SIDIS, indispensable for studies of the complex 3D nucleon structure, and discuss different components involved in precision extraction of the 3D partonic distribution and fragmentation functions.Extensive experimental measurements of spin and azimuthal asymmetries in various processes have stimulated theoretical interest and progress in the studies of the nucleon structure. The interpretation of experimental data in terms of parton distribution functions, generalized to describe transverse momentum and spatial parton distributions, is one of the main remaining challenges of modern nuclear physics. These new parton distribution and fragmentation functions encode the motion and the position of partons and are often referred to as three-dimensional distributions describing the three-dimensional (3D) structure of the nucleon. Understanding of the production mechanism and performing phenomenological studies compatible with factorization theorems using minimal model assumptions are goals of the analysis of the experimental data. HERMES and COMPASS Collaborations and experiments at Jefferson Lab have collected a wealth of polarized and unpolarized Semi-Inclusive Deep Inelastic Scattering (SIDIS) data. These data play a crucial role in current understanding of nucleon spin phenomena as they cover a broad kinematical range. The Jefferson Lab 12 GeV upgrade data on polarized and unpolarized SIDIS will have a remarkably higher precision at large parton fractional momentum $x$ compared to the existing data. We argue that both experimental and phenomenological communities will benefit from the development of a comprehensive extraction framework that will facilitate the extraction of the 3D nucleon structure, help understand various assumptions in extraction and data analysis, help to insure the model independence of the experimental data and validate the extracted functions. In this review we present the latest developments in the field of the spin asymmetries with emphasis on observables beyond the leading twist in SIDIS, indispensable for studies of the complex 3D nucleon structure, and discuss different components involved in precision extraction of the 3D partonic distribution and fragmentation functions.Extensive experimental measurements of spin and azimuthal asymmetries in various processes have stimulated theoretical interest and progress in the studies of the nucleon structure. The interpretation of experimental data in terms of parton distribution functions, generalized to describe transverse momentum and spatial parton distributions, is one of the main remaining challenges of modern nuclear physics. These new parton distribution and fragmentation functions encode the motion and the position of partons and are often referred to as three-dimensional distributions describing the three-dimensional (3D) structure of the nucleon. Understanding of the production mechanism and performing phenomenological studies compatible with factorization theorems using minimal model assumptions are goals of the analysis of the experimental data. HERMES and COMPASS Collaborations and experiments at Jefferson Lab have collected a wealth of polarized and unpolarized Semi-Inclusive Deep Inelastic Scattering (SIDIS) data. These data play a crucial role in current understanding of nucleon spin phenomena as they cover a broad kinematical range. The Jefferson Lab 12 GeV upgrade data on polarized and unpolarized SIDIS will have a remarkably higher precision at large parton fractional momentum $x$ compared to the existing data. We argue that both experimental and phenomenological communities will benefit from the development of a comprehensive extraction framework that will facilitate the extraction of the 3D nucleon structure, help understand various assumptions in extraction and data analysis, help to insure the model independence of the experimental data and validate the extracted functions. In this review we present the latest developments in the field of the spin asymmetries with emphasis on observables beyond the leading twist in SIDIS, indispensable for studies of the complex 3D nucleon structure, and discuss different components involved in precision extraction of the 3D partonic distribution and fragmentation functions.Extensive experimental measurements of spin and azimuthal asymmetries in various processes have stimulated theoretical interest and progress in studies of the nucleon structure. Interpretation of experimental data in terms of parton distribution functions, generalized to describe transverse momentum and spatial parton distributions, is one of the main remaining challenges of modern nuclear physics. These new parton distribution and fragmentation functions encode the motion and the position of partons and are often referred to as three-dimensional distributions describing the three-dimensional (3D) structure of the nucleon. Understanding of the production mechanism and performing phenomenological studies compatible with factorization theorems using minimal model assumptions are goals of analysis of the experimental data. HERMES and COMPASS Collaborations and experiments at Jefferson Lab have collected a wealth of polarized and unpolarized Semi-Inclusive Deep Inelastic Scattering (SIDIS) data. These data play a crucial role in current understanding of nucleon spin-phenomena as they cover a broad kinematical range. The Jefferson Lab 12 GeV upgrade data on polarized and unpolarized SIDIS will have remarkably higher precision at large parton fractional momentum $x$ compared to the existing data. We argue that both experimental and phenomenological communities will benefit from development of a comprehensive extraction framework that will facilitate extraction of 3D nucleon structure, help understand various assumptions in extraction and data analysis, help to insure the model independence of the experimental data and validate the extracted functions. In this review we present the latest developments in the field of the spin asymmetries and discuss different components involved in precision extraction of 3D partonic distribution and fragmentation functions.Extensive experimental measurements of spin and azimuthal asymmetries in various processes have stimulated theoretical interest and progress in the studies of the nucleon structure. The interpretation of experimental data in terms of parton distribution functions, generalized to describe transverse momentum and spatial parton distributions, is one of the main remaining challenges of modern nuclear physics. These new parton distribution and fragmentation functions encode the motion and the position of partons and are often referred to as three-dimensional distributions describing the three-dimensional (3D) structure of the nucleon. Understanding of the production mechanism and performing phenomenological studies compatible with factorization theorems using minimal model assumptions are goals of the analysis of the experimental data. HERMES and COMPASS Collaborations and experiments at Jefferson Lab have collected a wealth of polarized and unpolarized Semi-Inclusive Deep Inelastic Scattering (SIDIS) data. These data play a crucial role in current understanding of nucleon spin phenomena as they cover a broad kinematical range. The Jefferson Lab 12 GeV upgrade data on polarized and unpolarized SIDIS will have a remarkably higher precision at large parton fractional momentum x compared to the existing data. We argue that both experimental and phenomenological communities will benefit from the development of a comprehensive extraction framework that will facilitate the extraction of the 3D nucleon structure, help understand various assumptions in extraction and data analysis, help to insure the model independence of the experimental data and validate the extracted functions. In this review we present the latest developments in the field of the spin asymmetries with emphasis on observables beyond the leading twist in SIDIS, indispensable for studies of the complex 3D nucleon structure, and discuss different components involved in precision extraction of the 3D partonic distribution and fragmentation functions