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1.
《Nuclear Physics A》1997,627(4):679-709
In a model where constituent quarks and diquarks interact through quark exchange the Bethe-Salpeter equation in ladder approximation for the nucleon is solved. Quark and diquark confinement is effectively parametrized by choosing appropriately modified propagators. The coupling to external currents is implemented via non-trivial vertex functions for quarks and diquarks to ensure gauge invariance at the constituent level. Nucleon matrix elements are evaluated in a generalized impulse approximation, and electromagnetic, pionic and axial form factors are calculated. 相似文献
2.
In treating the relativistic 3-quark problem, a dressed-quark propagator parameterization is used which is compatible with
recent lattice data and pion observables. Furthermore 2-quark correlations are modeled as a series of quark loops in the scalar
and axialvector channel. The resulting reduced Faddeev equations are solved for nucleon and delta. Nucleon electromagnetic
form factors are calculated in a fully covariant and gauge-invariant scheme. Whereas the proton electric form factor G
E and the nucleon magnetic moments are described correctly, the neutron electric form factor and the ratio G
E/G
M for the proton appear to be quenched. The influence of vector mesons on the form factors is investigated which amounts to
a 25% modification of the electromagnetic proton radii within this framework.
Received: 16 April 2002 / Accepted: 29 August 2002 / Published online: 17 January 2003
RID="a"
ID="a"Supported by a Feodor-Lynen fellowship of the Alexander-von-Humboldt foundation and the Australian Research Council.
RID="b"
ID="b"Address after April 30: MPI für Metallforschung, Heisenbergstr. 1, 70569 Stuttgart, Germany.
RID="c"
ID="c"e-mail: Reinhard.Alkofer@uni-tuebingen.de
Communicated by A. Sch?fer 相似文献
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4.
D. Day 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):560-565
The nucleon form factors are still the subject of active investigation even after an experimental effort spanning 50 years.
This is because they are of critical importance to our understanding of the electromagnetic properties of nuclei and provide
a unique testing ground for QCD motivated models of nucleon structure. Progress in polarized beams, polarized targets and
recoil polarimetry have allowed an important and precise set of data to be collected over the last decade. I will review the
experimental status of elastic electron scattering from the nucleon along with an outlook for future progress. 相似文献
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6.
R. Alarcon the BLAST Collaboration 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):588-592
Measurements of the electric and magnetic form factors of the nucleon present a sensitive test of nucleon models and QCD-inspired
theories. A precise knowledge of the neutron form factors at low Q2 is also essential to reduce the systematic errors of parity violation experiments. At the MIT-Bates Linear Accelerator Center,
the nucleon form factors have been measured by means of scattering of polarized electrons from vector-polarized hydrogen and
deuterium. The experiment used the longitudinally polarized stored electron beam of the MIT-Bates South Hall Ring along with
an isotopically pure, highly vector-polarized internal atomic hydrogen and deuterium target provided by an atomic beam source.
The measurements have been carried out with the symmetric Bates Large Acceptance Spectrometer Toroid (BLAST) with enhanced
neutron detection capability. 相似文献
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9.
S.Pacetti 《中国物理C(英文版)》2010,34(6)
Analyticity of nucleon form factors allows to derive sum rules which,using space-like and time-like data as input,can give unique information about behaviors in energy regions not experimentally accessible.Taking advantage from new time-like data on proton-antiproton differential cross section and hence the possibility to separate electric and magnetic form factors also in the time-like region,we verify the consistency of the asymptotic behavior predicted by the perturbative QCD for the proton magnetic form factor. 相似文献
10.
S. Pacetti 《中国物理 C》2010,34(6):874-876
Analyticity of nucleon form factors allows to derive sum rules which, using space-like and time-like data as input, can give unique information about behaviors in energy regions not experimentally accessible. Taking advantage from new time-like data on proton-antiproton differential cross section and hence the possibility to separate electric and magnetic form factors also in the time-like region, we verify the consistency of the asymptotic behavior predicted by the perturbative QCD for the proton magnetic form factor. 相似文献
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12.
H. -W. Hammer 《The European Physical Journal A - Hadrons and Nuclei》2006,29(1):49-52
In the initial stage of the bottom-up picture of thermalization in heavy-ion collisions, the gluon distribution is highly
anisotropic which can give rise to plasma instability. This has not been taken into account in our original paper (Phys. Lett.
B 632, 257 (2006) hep-ph/0505164). It is shown that in the presence of instability there are scaling solutions, which depend on
one parameter, that match smoothly onto the late stage of bottom-up when thermalization takes place.-1 相似文献
13.
M. Oettel R. Alkofer L. von Smekal 《The European Physical Journal A - Hadrons and Nuclei》2000,8(4):553-566
In the covariant quark-diquark model the effective Bethe-Salpeter (BS) equations for the nucleon and the Δ are solved including
scalar and axial vector diquark correlations. Their quark substructure is effectively taken into account in both, the interaction kernel of the BS
equations and the currents employed to calculate nucleon observables. Electromagnetic current conservation is maintained.
The electric form factors of proton and neutron match the data. Their magnetic moments improve considerably by including axial
vector diquarks and photon induced scalar-axial vector transitions. The isoscalar magnetic moment can be reproduced, the isovector
contribution is about 15% too small. The ratio μG
E/G
M and the axial and strong couplings g
A, g
NN, provide an upper bound on the relative importance of axial vector diquarks confirming that scalar diquarks nevertheless
describe the dominant 2-quark correlations inside nucleons.
Received: 3 July 2000 / Accepted: 15 August 2000 相似文献
14.
The theoretical and experimental status of the isovector axial-vector current form factors G
A(q
2) and G
P(q
2) of the nucleon is reviewed. We also describe a new calculation of these form factors in manifestly Lorentz-invariant chiral
perturbation theory (ChPT) with the inclusion of axial-vector mesons as explicit degrees of freedom. 相似文献
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16.
Calculations of the proton and neutron charge form factors GEp,n(q2) are presented, based on chiral bag as well as confining Dirac potential models with chiral pion-quark coupling. Special emphasis is placed on a detailed treatment of the charged pion cloud contribution to the nucleon current. The role of a finite extension of the pion-quark vertex in truncating the summation over intermediate quark bag states is studied. Quark core radii (including recoil corrections) are constrained by a simultaneous calculation of the nucleon axial form factor. The proton charge form factor is well reproduced for with quark core rms radii between 0.5–0.6 fm. About of the proton charge is carried by the pion cloud in this model. The neutron charge form factor is obtained with the correct sign and overall q2 dependence but needs further refinements, probably at the level of the isoscalar form factor. 相似文献
17.
We provide a covariant, coordinate-free formulation of the many-dimensional Klein-Kramers equation for the phase space distribution of a Brownian particle. We construct a complete set of eigenfunctions of the collision operator adapted to the coordinate system, which involve covariant tensorial Hermite polynomials. The Klein-Kramers equation can then be reformulated as a system of coupled equations for the expansion coefficients with respect to this system. Truncation of this system of moment equations and application of a subsidiary condition yields a covariant generalization of Grad's thirteen-moment equations. As an application we give the explicit form of these equations for spherically symmetric, stationary solutions in spherical coordinates. We briefly comment on possible extensions of our treatment to slightly more complicated cases. 相似文献
18.
《Physics letters. [Part B]》1988,202(1):21-25
The nucleon magnetic moments and magnetic form factors have been calculated in the cloudy bag model. The πNN, πNΔ, γπ form factors and the CM corrections have been taken into account. We obtained very good results for these quantities. 相似文献
19.
We revisit F π(Q 2) and F Pγ(Q 2), P = π, η, η′, making use of the local-duality (LD) version of QCD sum rules. We give arguments that the LD sum rule provides reliable predictions for these form factors at Q 2 ≥ 5–6 GeV2, the accuracy of the method increasing with Q 2 in this region. For the pion elastic form factor, the well-measured data at small Q 2 give a hint that the LD limit may be reached already at relatively low values of momentum transfers, Q 2 ≈ 4–8 GeV2; we therefore conclude that large deviations from LD in the region Q 2 = 20–50 GeV2 seem very unlikely. The data on the (η, η′) → γγ* form factors meet the expectations from the LD model. However, the BaBar results for the π 0 → γγ* form factor imply a violation of LD growing with Q 2 even at Q 2 ≈ 40 GeV2, at odds with the η, η′ case and with the general properties expected for the LD sum rule. 相似文献
20.
Y.B. DongOn leave from Institute of High Energy Physics Academia Sinica Beijing P. R. China--> A. Faessler K. Shimizu 《The European Physical Journal A - Hadrons and Nuclei》1999,6(2):203-210
Electromagnetic form factors of protons and neutrons are investigated based on a relativistic quark model with the inclusion
of a pion cloud. Pseudo-scalar π-quark interaction is employed to study the coupling between the nucleon and the π. The results
show the important role of the pion cloud for the neutron charge form factor. Moreover, our numerical analysis indicates a
difference between the relativistic and the nonrelativistic treatments.
Received: 10 March 1999 / Revised version: 14 June 1999 相似文献