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Nucleon electromagnetic form factors and electroexcitation of low lying nucleon resonances in a light-front relativistic quark model

Description: We utilize a light-front relativistic quark model (LF RQM) to predict the 3q core contribution to the electroexcitation amplitudes for the {Delta}(1232)P{sub 33}, N(1440)P{sub 11}, N(1520)D{sub 13}, and N(1535)S{sub 11} up to Q{sup 2} = 12 GeV{sup 2}. The parameters of the model have been specified via description of the nucleon electromagnetic form factors in the approach that combines 3q and pion-cloud contributions in the LF dynamics.
Date: May 1, 2012
Creator: Aznauryan Inna, Burkert Volker
Partner: UNT Libraries Government Documents Department

An improved method for extracting matrix elements from lattice three-point functions

Description: The extraction of matrix elements from baryon three-point functions is complicated by the fact that the signal-to-noise drops rapidly as a function of time. Using a previously discussed method to improve the signal-to-noise for lattice two-point functions, we use this technique to do so for lattice three-point functions, using electromagnetic form factors for the nucleon and Delta as an example.
Date: December 1, 2011
Creator: C. Aubin, K. Orginos
Partner: UNT Libraries Government Documents Department

Current conservation and electromagnetic interaction currents for non-relativistic systems

Description: It is shown how to construct non-relativistic interaction currents which satisfy current conservation. The construction permits the use of different electromagnetic form factors for the pion, nucleon, and contact contributions, and therefore also permits the use of either G{sub E} of F{sub 1}. The numerical importance of this freedom for calculations of the electromagnetic form factors of {sup 3}He is studied, and found to be significant in some cases.
Date: May 1, 1991
Creator: Gross, Franz & Gross, Franz
Partner: UNT Libraries Government Documents Department

Measurements of the electromagnetic form factor of the Proton at Jlab

Description: The ratio of the proton's elastic electromagnetic form factors G{sub E{sub p}}/G{sub M{sub p}} was obtained by measuring P{sub t} and P{sub {ell}}, the transverse and longitudinal recoil proton polarization, respectively. For the elastic reaction {rvec e}p {yields} e{rvec p}, G{sub E{sub p}}/G{sub M{sub p}} is proportional to P{sub t}/P{sub {ell}}. The simultaneous measurement of P{sub t} and P{sub {ell}} in a polarimeter reduces systematic uncertainties. The results for the ratio G{sub E{sub p}}/G{sub M{sub p}} measured in Hall A so far show a systematic decrease with increasing Q{sup 2}, indicating for the first time a definite difference in the distribution of charge and magnetization in the proton. Together these experiments cover the Q{sub 2}- range of 0.5 to 5.6 GeV{sup 2}. A new experiment is currently being prepared, to extend the Q{sup 2}-range to 9 GeV{sup 2} in Hall C.
Date: April 1, 2003
Creator: Punjabi, Vina & Perdrisat, Charles
Partner: UNT Libraries Government Documents Department

Phenomenology of the deuteron electromagnetic form factors

Description: A rigorous extraction of the deuteron charge form factors from tensor polarization data in elastic electron-deuteron scattering, at given values of the 4-momentum transfer, is presented. Then the world data for elastic electron-deuteron scattering is used to parameterize, in three different ways, the three electromagnetic form factors of the deuteron in the 4-momentum transfer range 0-7 fm. This procedure is made possible with the advent of recent polarization measurements. The parameterizations allow a phenomenological characterization of the deuteron electromagnetic structure. They can be used to remove ambiguities in the form factors extraction from future polarization data.
Date: February 25, 2000
Creator: Abbott, David; Ahmidouch, Abdellah; Anklin, H.; Arvieux, J.; Ball, James P.; Beedoe, Shelton et al.
Partner: UNT Libraries Government Documents Department

Unified description of kaon electroweak form factors

Description: A calculation of the semileptonic decays of the kaon (K{sub l3}) is presented. The results are direct predictions of a covariant model of the pion and kaon introduced earlier by Ito, Buck, Gross. The weak form factors for K{sub l3} are predicted with absolutely no parameter adjustments of the model. The authors obtained for the form factor parameters: f{sub {minus}}(q{sup 2}=m{sub l}{sup 2})/f{sub +}(q{sup 2}=m{sub l}{sup 2})={minus}0.28 and {lambda}{sub +}= 0.028, both within experimental error bars. Connections of this approach to heavy quark symmetry will also be discussed.
Date: June 1, 1996
Creator: Afanasev, A. & Buck, W.
Partner: UNT Libraries Government Documents Department

Probing the structure of nucleons in the resonance region

Description: Status, open questions, and future prospects of the physics of excited nucleons are discussed. Emphasis is on the study of the structure of nucleons via measurements of their electromagnetic transition form factors, the search for ''missing'' resonances, the spin structure of the nucleon in the resonance region, and connections between the resonance and the deep-inelastic regimes.
Date: May 1, 2000
Creator: Burkert, Volker D.
Partner: UNT Libraries Government Documents Department

Flavor decomposition of the nucleon

Description: The author reviews some recent developments in the study of quark flavor distribution in the nucleon, including (1) valence quark distributions and quark-hadron duality prediction for the x {yields} 1 F{sup n}{sub 2}/F{sup p}{sub 2} ration (2) sea quark asymmetries and electromagnetic form factors (3) strange quarks in the nucleon.
Date: June 1, 1999
Creator: Melnitchouk, W.
Partner: UNT Libraries Government Documents Department

Introduction into QCD Sum Rule Approach

Description: In these lectures, I describe basic techniques of the QCD sum rule approach. The basic concepts of the approach are introduced using a simple model of quantum-mechanical oscillator in 2+1 dimensions. Then I discuss their field-theoretical extension and the construction of the operator product expansion for current correlators in QCD. The calculation of static parameters is illustrated on the example of sum rules in the vector and axial meson channels. Finally, the QCD sum rule calculation of the pion electromagnetic form factor is presented as an example of application of the method to dynamic characteristics of the hadrons.
Date: September 1, 1999
Creator: Radyushkin, A.
Partner: UNT Libraries Government Documents Department

QCD Calculations of Pion Electromagnetic and Transition Form Factors

Description: Summarizing both the perturbative and nonperturbative aspects of the Q{sup 2} dependence of the {gamma}{gamma}* {r_arrow} {pi}{sup 0} form factor and of the pion electromagnetic form factor are rather well understood in quantum chromodynamics. however, new experimental data at higher Q{sup 2} would be extremely helpful for detailed tests of the transition to the regime where the pQCD hard contribution plays the dominant role.
Date: April 1, 2001
Creator: Radyushkin, A.V.
Partner: UNT Libraries Government Documents Department

New constraints on dispersive form factor parameterizations from the timelike region

Description: The authors generalize a recent model-independent form factor parameterization derived from rigorous dispersion relations to include constraints from data in the timelike region. These constraints dictate the convergence properties of the parameterization and appear as sum rules on the parameters. They further develop a new parameterization that takes into account finiteness and asymptotic conditions on the form factor, and use it to fit to the elastic {pi} electromagnetic form factor. They find that the existing world sample of timelike data gives only loose bounds on the form factor in the spacelike region, but explain how the acquisition of additional timelike data or fits to other form factors are expected to give much better results. The same parameterization is seen to fit spacelike data extremely well.
Date: February 1, 1998
Creator: Buck, W. W. & Lebed, Richard F.
Partner: UNT Libraries Government Documents Department

Effective neutron targets

Description: Because of the lack of a free neutron target, deuterium targets have been used extensively in studying the neutron structure. The unique spin structure of the {sup 3}He ground state wave function and the recent developments in laser technologies made polarized {sup 3}He targets widely used in many experiments from neutron electromagnetic form factor studies to nucleon spin structure function measurements at all major electron accelerator facilities. In this talk, the current status of the polarized {sup 3}He targets will be reviewed. The author will focus on neutron electromagnetic form factor studies using polarized {sup 3}He targets. The polarized nucleon spin structure function measurements using polarized {sup 3}He targets will also be discussed.
Date: July 1, 1997
Creator: Gao, H.
Partner: UNT Libraries Government Documents Department

How well do we know the electromagnetic form factors of the proton?

Description: Recent measurements of recoil polarization in elastic scattering have been used to extract the ratio of the electric to the magnetic proton form factors. These results disagree with Rosenbluth extractions from cross section measurements, indicating either an inconsistency between the two techniques, or a problem with either the polarization transfer or cross section measurements. To obtain precise knowledge of the proton form factors, they must first understand the source of this discrepancy.
Date: September 24, 2002
Creator: Arrington, J.
Partner: UNT Libraries Government Documents Department

Nucleon Magnetic Form Factors

Description: A review of data on the nucleon electromagnetic form factors in the space-like region is presented. Recent results from experiments using polarized beams and polarized targets or nucleon recoil polarimeters have yielded a significant improvement on the precision of the data obtained with the traditional Rosenbluth separation. Future plans for extended measurements are outlined.
Date: December 1, 2001
Creator: Jager, Kees de
Partner: UNT Libraries Government Documents Department

Clean measurements of the nucleon axial-vector and free-neutron magnetic form factors

Description: We discuss the feasibility of a weak charged current experiment using a low energy electron beam. A first goal is to measure the Q^2 dependence of the axial-vector form factor g_a(Q^2). It can be measured model-independently and as robustly as for electromagnetic form factors from typical electron scattering experiments, in contrast to the methods used so far to measure g_a(Q^2). If g_a(Q^2) follows a dipole form, the axial mass can be extracted with a better accuracy than the world data altogether. The most important detection equipment would be a segmented neutron detector with good momentum and angular resolution that is symmetric about the beam direction, and covers a moderate angular range. A high intensity beam (100 uA) is necessary. Beam polarization is highly desirable as it provides a clean measurement of the backgrounds. Beam energies between 70 and 110 MeV are ideal. This range would provide a Q^2 mapping of g_a between 0.01
Date: November 1, 2013
Creator: Deur, Alexandre P.
Partner: UNT Libraries Government Documents Department

Nucleon Resonance Electrocouplings from the CLAS Meson Electroproduction Data.

Description: Transition helicity amplitudes {gamma}{sub {nu}}NN* (electrocouplings) were determined for prominent excited proton states with masses less than 1.8 GeV in independent analyses of major meson electroproduction channels: {pi}{sup +}n, {pi}{sup 0}p and {pi}{sup +}{pi}{sup -}p. Consistent results on resonance electrocouplings obtained from analyses of these exclusive reactions with very different non-resonant contributions demonstrated reliable extraction of these fundamental quantities for states that have significant decays for either N{pi} or N{pi}{pi} channels. Preliminary results on electrocouplings of N* states with masses above 1.6 GeV have become available from the CLAS data on {pi}{sup +}{pi}{sup -}p electroproduction off protons for the first time. Comparison with quark models and coupled channel approaches strongly suggest that N* structure is determined by contributions from an internal core of three constituent quarks and an external meson-baryon cloud at the distance scales covered in measurements with the CLAS detector.
Date: April 1, 2012
Creator: Inna Aznauryan, Volker Burkert, Viktor Mokeev
Partner: UNT Libraries Government Documents Department

Studies of Nucleon Form Factors with 12 GeV CEBAF and SuperBigBite

Description: The elastic electromagnetic form factors are among the most fundamental quantities that describe the ground-state structure of the proton and neutron. Precision data of the form factors over a wide kinematical range provide a powerful test of current theories of hadron structure. A number of experiments aiming to measure the electric and magnetic elastic form factors of the neutron, G{sub E}{sup n} and G{sub M}{sup n}, and proton, G{sub E}{sup p}, at very high momentum transfer, up to the range of Q{sup 2} = 10-14 (GeV/c){sup 2}, are planned to be carried out with the future 11 GeV electron beam of the upgraded CEBAF at Jefferson Lab. These experiments will determine the nucleon form factors with unprecedented precision to Q{sup 2}-values up to three times higher than those of existing data. We review the approved proposals and the conceptual design of a new spectrometer, SuperBigBite, that will be used in these and other future experiments at Jefferson Lab.
Date: April 1, 2012
Creator: Hansen, Jens-Ole
Partner: UNT Libraries Government Documents Department

Isoscalar Meson Exchange Currents and the Deuteron Form Factors

Description: The electromagnetic form factors for the RhoPiGamma and wSigmaGamma vertices are calculated from quark loop diagrams which take the qq structure of the Pi, Sigma, Rho, w mesons into account.The resulting form factors decrease with increasing Q<sup>2</sup> (the square of the four-momentum of the off-shell photon) considerably more rapidly than the monopole form factors obtained from vector meson dominance.The implications of this behavior, which has a significant effect on the elastic electromagnetic form factors of deuteron, is discussed.
Date: April 1, 1993
Creator: Gross, Franz & Gross, Franz
Partner: UNT Libraries Government Documents Department

Recent results for (e,e{prime}p) reactions at Jefferson Lab

Description: Coincidence cross sections for (e, e{prime}p) quasi-elastic scattering were measured at CEBAF with high statistical precision for C, Fe, and Au targets for 0.6 < Q{sup 2} < 3.3 GeV{sup 2}. Missing energy and missing momentum distributions obtained from a preliminary analysis are in reasonable agreement with prior data from SLAC. The preliminary analysis are compared with a PWIA calculation to determine the nuclear transparency as a function of Q{sup 2} and A. A Rosenbluth analysis to extract the longitudinal and transverse cross sections from these data is anticipated.
Date: September 1, 1997
Creator: Potterveld, D.; Cummings, W.J. & Geesaman, D.F.
Partner: UNT Libraries Government Documents Department

Precise measurement of the neutron magnetic form factor from quasielastic {sup 3}{rvec H}e({rvec e},e`)

Description: Polarized {sup 3}He targets have proven to be a useful tool for studying the electric and magnetic form factors of the neutron, and the spin structure of the neutron. The neutron magnetic form factor at low Q{sup 2} was determined previously at MIT-Bates from the quasielastic {sup 3}{ital {rvec H}e({rvec e}, e{sup `})} process. New experiment was planned at TJNAF to systematically measure the inclusive {sup 3}He quasielastic transverse asymmetry, A{sub T{sup `}}, at Q{sup 2} = 0.1 - 0.5 (GeV/c){sup 2} with high statistical and systematic accuracy. A 2% statistical uncertainty is aimed at all the pro- posed values of Q{sup 2} , and 3% systematic uncertainty for A{sub T{sup `}} can be achieved for this experiment. The precise data will constrain theoretical calculations of {sup 3}He quasielastic asymmetry. Furthermore, the neutron magnetic form factor at Q{sup 2} = 0.1 - 0.5 (GeV/c){sup 2} will be extracted from the measured asymmetries with an overall uncertainty of 2%. Precise measurements of {ital G{sup n}{sub M}} at low Q{sup 2} will resolve the discrepancy among the existing data in the same Q{sup 2} region.
Date: February 1, 1997
Creator: Gao, H.
Partner: UNT Libraries Government Documents Department

Local duality predictions for x {approx} 1 structure functions

Description: Recent data on the proton F{sub 2} structure function in the resonance region suggest that local quark-hadron duality works remarkably well for each of the low-lying resonances, including the elastic, to rather low values of Q{sup 2}. The authors discuss model-independent relations between structure functions x{approx}1 and elastic electromagnetic form factors. The x{yields}1 behavior of the nucleon polarization asymmetries and the neutron to proton structure function ratios is studied as a function of Q-squared using available data on the electric and magnetic form factors.
Date: March 24, 2000
Creator: Melnitchouk, W.
Partner: UNT Libraries Government Documents Department

Nucleon electromagnetic form factors

Description: A review of data on the nucleon electromagnetic form factors in the space-like region is presented. Recent results from experiments using polarized beams and polarized targets or nucleon recoil polarimeters have yielded a significant improvement on the precision of the data obtained with the traditional Rosenbluth separation. Future plans for extended measurements are outlined.
Date: January 1, 2000
Creator: Jager, Kees de
Partner: UNT Libraries Government Documents Department

Strange vector currents and the OZI-rule

Description: The authors investigate the role of correlated {pi}{rho} exchange in the extraction of matrix elements of the strange vector current in the proton. They show that a realistic isoscalar spectral function including this effect leads to sizably reduced strange vector form factors based on the dispersion--theoretical analysis of the nucleons' electromagnetic form factors.
Date: January 1, 1997
Creator: Meisner, U.; Mull, V.; Speth, J. & Orden, J. Van
Partner: UNT Libraries Government Documents Department