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Extracting TMDs from CLAS12 data

Description: We present studies of double longitudinal spin asymmetries in semi-inclusive deep inelastic scattering using a new dedicated Monte Carlo generator, which includes quark intrinsic transverse momentum within the generalized parton model based on the fully differential cross section for the process. Additionally we employ Bessel-weighting to the MC events to extract transverse momentum dependent parton distribution functions and also discuss possible uncertainties due to kinematic correlation effects.
Date: January 1, 2014
Creator: Aghasyan, Mher M. & Avakian, Harut A.
Partner: UNT Libraries Government Documents Department

Extraction of Transversity and Collins Functions

Description: We present a global re-analysis of recent experimental data on azimuthal asymmetries in semi-inclusive deep inelastic scattering, from the HERMES and COMPASS Collaborations, and in e{sup +}e{sup -} --> h_1h_2X processes, from the Belle Collaboration. The transversity distribution and the Collins functions are extracted simultaneously, in a revised analysis which also takes into account a new parameterization of the unknown functions.
Date: January 1, 2014
Creator: Anselmino, Mauro; Boglione, Mariaelena; D'Alesio, Umberto; Melis, Stefano; Murgia, Francesco & Prokudin, Alexei
Partner: UNT Libraries Government Documents Department

Extractions of polarized and unpolarized parton distribution functions

Description: An overview of our ongoing extractions of parton distribution functions of the nucleon is given. First JAM results on the determination of spin-dependent parton distribution functions from world data on polarized deep-inelastic scattering are presented first, and followed by a short report on the status of the JR unpolarized parton distributions. Different aspects of PDF analysis are briefly discussed, including effects of the nuclear structure of targets, target-mass corrections and higher twist contributions to the structure functions.
Date: January 1, 2014
Creator: Jimenez-Delgado, Pedro
Partner: UNT Libraries Government Documents Department

First JAM results on the determination of polarized parton distributions

Description: The Jefferson Lab Angular Momentum (JAM) Collaboration is a new initiative to study the angular momentum dependent structure of the nucleon. First results on the determination of spin-dependent parton distribution functions at intermediate and large x from world data on polarized deep-inelastic scattering are presented. Different aspects of global QCD analysis are discussed, including the effects of nuclear structure of deuterium and {sup 3}He targets, target mass corrections and higher twist contributions to the g{sub 1} and g{sub 2} structure functions.
Date: January 1, 2014
Creator: Accardi, Alberto; Jimenez-Delgado, Pedro & Melnitchouk, Wally
Partner: UNT Libraries Government Documents Department

Global Analysis Of The Negative Parity Non-Strange Baryons In The 1/N{sub c} Expansion

Description: A global study of the negative parity non-strange baryon observables is performed in the framework of the 1/N{sub c} expansion. Masses, partial decay widths and photo-couplings are simultaneously analyzed. A main objective is to determine the composition of the spin 1/2 and 3/2 nucleon states, which come in pairs and involve two mixing angles which can be determined and tested for consistency by the mentioned observables. The issue of the assignment of those nucleon states to the broken SU(4) X O(3) mixed-symmetry multiplet is studied in detail, with the conclusion that the assignment made in the old studies based on the non-relativistic quark model is the preferred one. In addition, the analysis involves an update of the input data with respect to previous works.
Date: February 1, 2014
Creator: Goity, Jose L.; Hampton University, Hampton, VA (United States)]; Gonzalez de Urreta, Emiliano Jose; CONICET, Rivadavia 1917, (1033) Buenos Aires (Argentina)]; Scoccola, Norberto N.; CONICET, Rivadavia 1917, (1033) Buenos Aires (Argentina) et al.
Partner: UNT Libraries Government Documents Department

Measurement Of Differential Cross Sections Of p(e,e'{pi}{sup +})n For High-Lying Resonances At Q{sup 2} < 5 GeV{sup 2}

Description: The exclusive electro-production process $ep\to e^{\prime}n\pi^+$ was measured in the range of the invariant mass for $n\pi^+$ system $1.6~\rm{GeV}\le W \le 2.0~\rm{GeV}$, and the photon virtuality $1.8~\rm{GeV^2}\le Q^2\le4.0~\rm{GeV^2}$ using CLAS. For the first time, these kinematics are probed in exclusive $\pi^+$ production from the protons with nearly full coverage in the azimuthal and polar angles of the $n\pi^+$ center-of-mass system. In this experiment, approximately 39,000 differential cross-section data points were measured. In this proceeding, preliminary results of our latest analysis work are presented on differential cross sections and structure functions as well as Legendre Moments.
Date: January 1, 2014
Creator: Park, Kijun
Partner: UNT Libraries Government Documents Department

Measurement of Excited Hyperons in Photoproduction at CLAS

Description: Measurement results of photoproduced excited hyperon states using the CLAS detector at Jefferson Lab are shown. The invariant mass distribution of the {Lambda}(1405) has recently been shown to be different for each of the three Sigma pi channels that it decays to, showing that there is prominent interference between the isospin I=0 and I=1 isospin amplitudes. Measurements of the differential and total cross sections of the three hyperons {Lambda}(1405), {Sigma}{sup 0}(1385), and Lambda(1520) are presented and compared. Prospects of future studies using a 12 GeV beam with the GlueX detector are briefly given.
Date: January 1, 2014
Creator: Moriya, Kei & Schumacher, Reinhard A.
Partner: UNT Libraries Government Documents Department

Measurements Of Spin Observables In Pseudoscalar-Meson Photo-Production Using Polarized Neutrons In Solid HD

Description: Psuedo-scalar meson photo production measurements have been carried out with longitudinally-polarized neutrons using the circularly and linearly polarized photon beams and the CLAS at Thomas Jefferson National Accelerator Facility (Jlab). The experiment aims to obtain a complete set of spin observables on an efficient neutron target. Preliminary E asymmetries for the exclusive reaction, gamma + n(p)--> pi- + p(p), selecting quasi free neutron kinematics are discussed.
Date: January 1, 2014
Creator: Kageya, Tsuneo
Partner: UNT Libraries Government Documents Department

New model for nucleon generalized parton distributions

Description: We describe a new type of models for nucleon generalized parton distributions (GPDs) H and E. They are heavily based on the fact nucleon GPDs require to use two forms of double distribution (DD) representations. The outcome of the new treatment is that the usual DD+D-term construction should be amended by an extra term, {xi} E{sub +}{sup 1} (x,{xi}) which has the DD structure {alpha}/{beta} e({beta},{alpha}, with e({beta},{alpha}) being the DD that generates GPD E(x,{xi}). We found that this function, unlike the D-term, has support in the whole -1 <= x <= 1 region. Furthermore, it does not vanish at the border points |x|={xi}.
Date: January 1, 2014
Creator: Radyushkin, Anatoly V.
Partner: UNT Libraries Government Documents Department

On the role of the Sivers effect in A{sub N} for inclusive particle production in pp collisions

Description: Single spin asymmetries, A{sub N} , for inclusive particle production in pp collisions are considered within a generalized parton model with inclusion of spin and tranverse momentum effects. We consider the potential role of the Sivers effect in A{sub N} , as extracted from a careful analysis of azimuthal asymmetries in SIDIS, and discuss its phenomenological consequences in connection with a recently updated study of the Collins effect.
Date: January 1, 2014
Creator: Anselmino, Mauro; Boglione, Mariaelena; D'Alesio, Umberto; Melis, Stefano; Murgia, Francesco & Prokudin, Alexei
Partner: UNT Libraries Government Documents Department

Chiral dynamics and peripheral transverse densities

Description: In the partonic (or light-front) description of relativistic systems the electromagnetic form factors are expressed in terms of frame-independent charge and magnetization densities in transverse space. This formulation allows one to identify the chiral components of nucleon structure as the peripheral densities at transverse distances b = O(M{sub {pi}}{sup -1}) and compute them in a parametrically controlled manner. A dispersion relation connects the large-distance behavior of the transverse charge and magnetization densities to the spectral functions of the Dirac and Pauli form factors near the two--pion threshold at timelike t = 4 M{ sub {pi}}{sup 2}, which can be computed in relativistic chiral effective field theory. Using the leading-order approximation we (a) derive the asymptotic behavior (Yukawa tail) of the isovector transverse densities in the "chiral" region b = O(M{sub {pi}}{sup -1}) and the "molecular" region b = O(M{sub N}{sup 2}/M{sub {pi}}{sup 3}); (b) perform the heavy-baryon expansion of the transverse densities; (c) explain the relative magnitude of the peripheral charge and magnetization densities in a simple mechanical picture; (d) include Delta isobar intermediate states and study the peripheral transverse densities in the large-N{ sub c} limit of QCD; (e) quantify the region of transverse distances where the chiral components of the densities are numerically dominant; (f) calculate the chiral divergences of the b{sup 2}-weighted moments of the isovector transverse densities (charge and anomalous magnetic radii) in the limit M{sub {pi}} -> 0 and determine their spatial support. Our approach provides a concise formulation of the spatial structure of the nucleon's chiral component and offers new insights into basic properties of the chiral expansion. It relates the information extracted from low-t elastic form factors to the generalized parton distributions probed in peripheral high-energy scattering processes.
Date: January 1, 2014
Creator: Granados, Carlos G. & Weiss, Christian
Partner: UNT Libraries Government Documents Department

Polarization Observables From The Photoproduction Of Omega-Mesons Using Linearly Polarized Photons

Description: We report on the extraction of Polarization Observables Spin Density Matrix Elements (SDMEs), and Beam Asymmetry Sigma for omega meson photoproduction using a beam of linearly polarized photons in the photon energy region of Egamma = 1.3 to 1.7 GeV, by means of the angular distributions of the daughter pions from omega decay. These preliminary results are from the g8b dataset, which were collected with the CLAS detector in Hall B of Jefferson Lab.
Date: January 1, 2014
Creator: Martinez, Danny & Cole, Philip L.
Partner: UNT Libraries Government Documents Department

QCD Condensates and Holographic Wilson Loops for Asymptotically AdS Spaces

Description: The minimization of the Nambu-Goto (NG) action for a surface whose contour defines a circular Wilson loop of radius a placed at a finite value of the coordinate orthogonal to the border is considered. This is done for asymptotically AdS spaces. The condensates of dimension n = 2, 4, 6, 8, and 10 are calculated in terms of the coefficients in the expansion in powers of the radius a of the on-shell subtracted NG action for small a->0. The subtraction employed is such that it presents no conflict with conformal invariance in the AdS case and need not introduce an additional infrared scale for the case of confining geometries. It is shown that the UV value of the gluon condensates is universal in the sense that it only depends on the first coefficients of the difference with the AdS case.
Date: February 1, 2014
Creator: Quevedo, R. Carcasses; CONICET, Rivadavia 1917, 1033 Buenos Aires (Argentina)]; Goity, Jose L.; Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)]; Trinchero, Roberto C. & CONICET, Rivadavia 1917, 1033 Buenos Aires (Argentina)]
Partner: UNT Libraries Government Documents Department

Sea quark transverse momentum distributions and dynamical chiral symmetry breaking

Description: Recent theoretical studies have provided new insight into the intrinsic transverse momentum distributions of valence and sea quarks in the nucleon at a low scale. The valence quark transverse momentum distributions (q - qbar) are governed by the nucleon's inverse hadronic size R{sup -1} ~ 0.2 GeV and drop steeply at large p{sub T}. The sea quark distributions (qbar) are in large part generated by non-perturbative chiral-symmetry breaking interactions and extend up to the scale rho{sup -1} ~ 0.6 GeV. These findings have many implications for modeling the initial conditions of perturbative QCD evolution of TMD distributions (starting scale, shape of p{sub T}. distributions, coordinate-space correlation functions). The qualitative difference between valence and sea quark intrinsic p{sub T}. distributions could be observed experimentally, by comparing the transverse momentum distributions of selected hadrons in semi-inclusive deep-inelastic scattering, or those of dileptons produced in pp and pbar-p scattering.
Date: January 1, 2014
Creator: Schweitzer, Peter; Strikman, Mark & Weiss, Christian
Partner: UNT Libraries Government Documents Department

Studies of N*#3; Structure from the CLAS Meson Electroproduction Data

Description: The transition {gamma}{sub v}pN#3; amplitudes (electrocouplings) for prominent excited nucleon states obtained in a wide area of photon virtualities offer valuable information for the exploration of the N#3; structure at different distances and allow us to access the complex dynamics of non-perturbative strong interaction. The current status in the studies of {gamma}{sub v}pN#3; electrocouplings from the data on exclusive meson electroproduction off protons measured with the CLAS detector at Jefferson Lab is presented. The impact of these results on exploration of the N#3; structure is discussed.
Date: January 1, 2014
Creator: Mokeev, Viktor I. & Aznauryan, Inna G.
Partner: UNT Libraries Government Documents Department

Studies of the 3D structure of the proton at Jlab

Description: 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.
Date: January 1, 2014
Creator: Avakian, Harut A.
Partner: UNT Libraries Government Documents Department

Study of excited nucleons and their structure

Description: Recent advances in the study of excited nucleons are discussed. Much of the progress has been achieved due to the availability of high precision meson production data in the photoproduction and electroproduction sectors, the development of multi-channel partial wave analysis techniques, and advances in Lattice QCD with predictions of the full excitation spectrum.
Date: January 1, 2014
Creator: Burkert, Volker D.
Partner: UNT Libraries Government Documents Department

Transition Form Factors: A Unique Opportunity to Connect #11;Non-Perturbative Strong Interactions to QCD

Description: Meson-photoproduction measurements and their reaction-amplitude analyses can establish more sensitively, and in some cases in an almost model-independent way, nucleon excitations and non-resonant reaction amplitudes. However, to investigate the strong interaction from explored — where meson-cloud degrees of freedom contribute substantially to the baryon structure — to still unexplored distance scales — where quark degrees of freedom dominate and the transition from dressed to current quarks occurs — we depend on experiments that allow us to measure observables that are probing this evolving non-perturbative QCD regime over its full range. Elastic and transition form factors are uniquely suited to trace this evolution by measuring elastic electron scattering and exclusive single-meson and double-pion electroproduction cross sections off the nucleon. These exclusive measurements will be extended to higher momentum transfers with the energy-upgraded CEBAF beam at JLab to study the quark degrees of freedom, where their strong interaction is responsible for the ground and excited nucleon state formations. After establishing unprecedented high-precision data, the imminent next challenge is a high-quality analysis to extract these relevant electrocoupling parameters for various resonances that then can be compared to state-of-the-art models and QCD-based calculations. Recent results will demonstrate the status of the analysis and of their theoretical descriptions, and an experimental and theoretical outlook will highlight what shall and may be achieved in the new era of the 12-GeV upgraded transition form factor program.
Date: January 1, 2014
Creator: Gothe, Ralf W.
Partner: UNT Libraries Government Documents Department

Transverse charge and magnetization densities in the nucleon's chiral periphery

Description: In the light-front description of nucleon structure the electromagnetic form factors are expressed in terms of frame-independent transverse densities of charge and magnetization. Recent work has studied the transverse densities at peripheral distances b = O(M{pi}{sup -1}), where they are governed by universal chiral dynamics and can be computed in a model-independent manner. Of particular interest is the comparison of the peripheral charge and magnetization densities. We summarize (a) their interpretation as spin-independent and -dependent current matrix elements; (b) the leading-order chiral effective field theory results; (c) their mechanical interpretation in the light-front formulation; (d) the large-N_c limit of QCD and the role of {Delta} intermediate states; (e) the connection with generalized parton distributions and peripheral high-energy scattering processes.
Date: January 1, 2014
Creator: Granados, Carlos G. & Weiss, Christian
Partner: UNT Libraries Government Documents Department

Studies of Charged Particle Dynamics for Antihydrogen Synthesis

Description: Synthesis and capture of antihydrogen in controlled laboratory conditions will enable precise studies of neutral antimatter. The work presented deals with some of the physics pertinent to manipulating charged antiparticles in order to create neutral antimatter, and may be applicable to other scenarios of plasma confinement and charged particle interaction. The topics covered include the electrostatic confinement of a reflecting ion beam and the transverse confinement of an ion beam in a purely electrostatic configuration; the charge sign effect on the Coulomb logarithm for a two component (e.g., antihydrogen) plasma in a Penning trap as well as the collisional scattering for binary Coulomb interactions that are cut off at a distance different than the Debye length; and the formation of magnetobound positronium and protonium.
Date: December 2014
Creator: Correa, Jose Ricardo
Partner: UNT Libraries