520 Matching Results

Search Results

Advanced search parameters have been applied.

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

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

Heavy quark symmetries and the decays baryon antibaryon

Description: We enumerate the form factors necessary to describe the two-body baryonic decays of B mesons.We use the symmetries of the heavy quark effective theory to arrive at some relations among these form factors, when at least one of the daughter baryons is heavy.
Date: October 1, 1991
Creator: Roberts, Winston; Roberts, Winston & Ryzak, Z.
Partner: UNT Libraries Government Documents Department

The heavy expansion in B decays

Description: We examine the 1/mc and 1/mb expansions in B^(*)->D^(*) processes, and point out that there are relationships among the form factors that do not receive corrections in any order of 1/mc.A different set of relationships are unchanged by (1/mc)^n corrections, while the (1/mc)^n preserved relationships are also unaffected by terms proportional to powers of Alphas(mc).All relationships are modified when terms of the form 1/(mbmc) or radiative corrections proportional to powers of Alphas(mb) are included.
Date: August 1, 1993
Creator: Roberts, Winston & Roberts, Winston
Partner: UNT Libraries Government Documents Department

1/m<sub>c</sub> Terms in lambda<sup>+</sup><sub>c</sub> Semileptonic Decays

Description: We use the heavy quark effective theory to investigate the form factors that describe the semileptonic decays lambda<sup>+</sup><sub>c</sub> -> lambda e<sup>+</sup> nu, to order 1/m<sub>c</sub>. We find that a total of four form factors are needed to this order, in contrast with two form factors to leading order, and six form factors in the most general case. We point out some relationships that arise among the general form factors.
Date: February 1, 1992
Creator: Roberts, Winston
Partner: UNT Libraries Government Documents Department

The axial anomaly and the dynamical breaking of chiral symmetry

Description: Using the quark triangle diagram for the Adler-Bell-Jackiw axial anomaly, we calculate the form factor for the {gamma}{sup *}{pi}{sup 0}{yields}{gamma} transition. This form factor depends on the quark mass, and we predict the right behavior with m{sub q}{approx_equal}250 MeV, the same quark mass generated by the dynamical breaking of chiral symmetry through a Nambu-Jona-Lasinio mechanism.
Date: October 1, 1991
Creator: Gross, Franz; Ito, Hiroshi & Buck, Warren
Partner: UNT Libraries Government Documents Department

Finite Size Effects on the Real-Space Pair Distribution Function of Nanoparticles

Description: The pair distribution function (PDF) method is a powerful approach for the analysis of the structure of nanoparticles. An important approximation used in nanoparticle PDF simulations is the incorporation of a form factor describing nanoparticle size and shape. The precise effect of the form factor on the PDF is determined by both particle shape and structure if these characteristics are both anisotropic and correlated. The correct incorporation of finite size effects is important for distinguishing and quantifying the structural consequences of small particle size in nanomaterials.
Date: October 1, 2008
Creator: Gilbert, Benjamin
Partner: UNT Libraries Government Documents Department

The Pion Form-Factor

Description: The experimental situation with regard to measurements of the pion charge form factor is reviewed. Both existing data and planned experiments are discussed.
Date: May 1, 2002
Creator: Blok, H.P.; Huber, G.M. & Mack, D.J.
Partner: UNT Libraries Government Documents Department

Measurement of G

Description: The ratio of the electric and magnetic form factors of the proton, G{sub E{sub p}}/G{sub M{sub p}}, was measured at the Thomas Jefferson National Accelerator Facility (JLab) using the recoil polarization technique. The ratio of the form factors is directly proportional to the ratio of the transverse to longitudinal components of the polarization of the recoil proton in the elastic {rvec e}p {yields} e{rvec p} reaction. The new data presented in this article span the range 3.5 &lt; Q{sup 2} &lt; 5.6 GeV{sup 2} and are well described by a linear Q{sup 2} fit. Also, the ratio QF{sub 2p}/F{sub 1p} reaches a constant value above Q{sup 2}=2 GeV{sup 2}.
Date: March 1, 2002
Creator: Gayou, Olivier; Brash, Ed J.; Jones, Mark K.; Perdrisat, Charles F.; Punjabi, Vina; Pentchev, L. et al.
Partner: UNT Libraries Government Documents Department

B {right arrow}Dl{nu}form factors and the Determination of |V{sub cb}|

Description: The zero recoil limit of the B{yields}Dl{nu} form factors is calculated on the lattice, which provides a model-independent determination of {vert_bar}V{sub cb}{vert_bar}. Considering a ratio of form factors, in which the bulk of statistical and systematic errors cancel, we obtain a precise result both for h{sub +}(1) and for h{sub -}(1).
Date: November 1, 1998
Creator: al., S.Hashimoto et
Partner: UNT Libraries Government Documents Department

Off-forward parton distribution

Description: Recent developments in studying off-forward parton distributions are discussed. In this talk, the author discusses the recent developments in studying the off-forward parton distributions (OFPD`s). He has written a topical review article on the subject, which will soon be published in Journal of Physics G. The interested audience can consult that article for details. His talk consists of three parts: definition of the new distributions, their physical significance, and experimental measurements.
Date: December 1, 1998
Creator: Ji, X.
Partner: UNT Libraries Government Documents Department

{epsilon}{prime}/{epsilon} and rare KL decays from KTeV Experiment

Description: The authors update the current status for the measurement of the direct-CP violation parameters {epsilon}{prime}/{epsilon} in the KTeV experiment at Fermilab. Substantial statistics have been accumulated during the 1996-7 run and 1999 run for both {epsilon}{prime}/{epsilon} and rare K{sub L} decay searches. The first KTeV result on {epsilon}{prime}/{epsilon} published last year was Re({epsilon}{prime}/{epsilon}) = (28.0 {+-} 4.1) x 10{sup {minus}4} based on the 23% data from 1996-7 run. Combining with the previous E731, NA31 and the recent preliminary NA48 results, the grand average is Re({epsilon}{prime}/{epsilon}) = (19.3 {+-} 3.6) x 10{sup {minus}4} (with S = 1:49), more than 5{sigma} above zero. More data from both KTeV and NA48 after completing the analysis will further improve the precision of this measurement in the near future and hopefully further improve the agreement. New results on the branching ratio and form factor measurements of K{sub L} {r_arrow} {mu}{sup +} {mu}{sup {minus}} {gamma} using 1997 data are also presented. We find that BR(K{sub L} {r_arrow} {mu}{sup +} {mu}{sup {minus}} {gamma}) = (3.66 {+-} 0.04{sub stat} {+-} 0.07{sub syst}) x 10{sup {minus}7}. The form factor parameter {alpha}{sub K}* is measured to be {alpha}{sub K}* = {minus}0.157{sub {minus}0.027}{sup +0.025}. We make the first measurement of the parameter {alpha} from the D'Ambrosio, Isidori, and Portoles form factor, finding {alpha} = {minus}1.53 {+-} 0.09. This measurement of {alpha} limits the CKM parameter {rho} &gt; {minus}0.2.
Date: January 16, 2001
Creator: Hsiung, Yee Bob
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

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

QCD constraints on form factor shapes

Description: This talk presents an introduction to the use of dispersion relations to constrain the shapes of hadronic form factors consistent with QCD. The applications described include methods for studying the strange quark mass,and the pion charge ratio.
Date: May 20, 1999
Creator: Lebed, R.F.
Partner: UNT Libraries Government Documents Department

Realizing vector meson dominance with transverse charge densities

Description: The transverse charge density in a fast-moving nucleon is represented as a dispersion integral of the imaginary part of the Dirac form factor in the timelike region (spectral function). At a given transverse distance b the integration effectively extends over energies in a range {radical}t {approx}&lt; 1/b, with exponential suppression of larger values. The transverse charge density at peripheral distances thus acts as a low-pass filter for the spectral function and allows one to select energy regions dominated by specific t-channel states, corresponding to definite exchange mechanisms in the spacelike form factor. We show that distances b {approx} 0.5 - 1.5 fm in the isovector density are maximally sensitive to the {rho} meson region, with only a {approx}10% contribution from higher-mass states. Soft-pion exchange governed by chiral dynamics becomes relevant only at larger distances. In the isoscalar density higher-mass states beyond the {omega} are comparatively more important. The dispersion approach suggests that the positive transverse charge density in the neutron at b {approx} 1 fm, found previously in a Fourier analysis of spacelike form factor data, could serve as a sensitive test of the isoscalar strength in the {approx}1 GeV mass region. In terms of partonic structure, the transverse densities in the vector meson region b {approx} 1 fm support an approximate mean-field picture of the motion of valence quarks in the nucleon.
Date: October 1, 2011
Creator: Gerald Miller, Mark Strikman, Christian Weiss
Partner: UNT Libraries Government Documents Department

Perturbative QCD and Electromagnetic Form Factors

Description: We calculate nucleon magnetic form factors using perturbative QCD for several distribution amplitudes including a general one given in terms of Appell polynomials. We find that the magnitude and sign of both nucleon magnetic form factors can be explained within perturbative QCD. The observed normalization of GMp requires that the disturbution amplitude be broader than its superhigh momentum transfer limit, and the GMn/GMp data may require the distrubution amplitude to be asymmetric, in accord with distribution amplitudes derived from QCD sum rules. Some speculation as to how an asymmetric distribution amplitude can come about is offered. Finally, we show that the soft contribution corresponding to the particular distribution amplitudes we use need not be bigger than the data.
Date: October 1, 1987
Creator: Carlson, Carl & Gross, Franz
Partner: UNT Libraries Government Documents Department

The Charge Form Factors of the Three- and Four-Body Nuclei

Description: The charge form factors of 3H, 3He, and 4He are calculated using the Monte Carlo method and variational ground-state wave functions obtained for the Argonne two-nucleon and Urbana-VII three-nucleon interactions. The model for the charge density operator contains the two-body exchange contributions of longest range. With some spread due to the uncertainty in the electromagnetic form factors of the nucleon the calculated charge form factors are in good agreement with the empirical values over the whole experimentally covered range of momentum transfer.
Date: January 1, 1990
Creator: Schiavilla, R.; Pandharipande, V.R. & Riska, D.O.
Partner: UNT Libraries Government Documents Department

Nucleon Electromagnetic Form Factors

Description: There has been much activity in the measurement of the elastic electromagnetic proton and neutron form factors in the last decade, and the quality of the data has greatly improved by performing double polarization experiments, in comparison with previous unpolarized data. Here we review the experimental data base in view of the new results for the proton, and neutron, obtained at JLab, MAMI, and MIT-Bates. The rapid evolution of phenomenological models triggered by these high-precision experiments will be discussed, including the recent progress in the determination of the valence quark generalized parton distributions of the nucleon, as well as the steady rate of improvements made in the lattice QCD calculations.
Date: October 1, 2007
Creator: Vanderhaeghen, Marc; Perdrisat, Charles & Punjabi, Vina
Partner: UNT Libraries Government Documents Department

Precision Rosenbluth Measurement of the Proton Elastic Electromagnetic Form Factors and Their Ratio at Q^2=2.64, 3.20, and 4.10 GeV^2

Description: Due to the inconsistency in the results of the mupGEp/GMp ratio of the proton, as extracted from the Rosenbluth and recoil polarization techniques, high precision measurements of the e-p elastic scattering cross sections were made at Q{sup 2} = 2.64, 3.20, and 4.10 GeV{sup 2}. Protons were detected, in contrast to previous measurements where the scattered electrons were detected, which dramatically decreased-dependent systematic uncertainties and corrections. A single spectrometer measured the scattered protons of interest while simultaneous measurements at Q{sup 2} = 0.5 GeV{sup 2} were carried out using another spectrometer which served as a luminosity monitor in order to remove any uncertainties due to beam charge and target density fluctuations. The absolute uncertainty in the measured cross sections is {approx}3% for both spectrometers and with relative uncertainties, random and slope, below 1% for the higher Q{sup 2} protons, and below 1% random and 6% slope for the monitor spectrometer. The extracted electric and magnetic form factors were determined to 4%-7% for GEp and 1.5% for GMp. The ratio mupGEp/GMp was determined to 4%-7% and showed mupGEp/GMp {approx} 1.0. The results of this work are in agreement with the previous Rosenbluth data and inconsistent with high-Q{sup 2} recoil polarization results, implying a systematic difference between the two techniques.
Date: December 1, 2005
Creator: Qattan, Issam A.
Partner: UNT Libraries Government Documents Department

Nonlocal Condensates and QCD Sum Rules for the Pion Form Factor

Description: We extend the QCD sum rule analysis of the pion electromagnetic form factor F(sub)pi(Q^2) into the region of moderately large momentum transfers 3GeV^2 < Q^2 < 10 GeV^2, where one should take into account the effects due to nonzero average virtuality of the vacuum quarks and gluons.
Date: October 1, 1991
Creator: Radyushkin, Anatoly & Radyushkin, Anatoly
Partner: UNT Libraries Government Documents Department