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1.
D. Merten U. Löring K. Kretzschmar B. Metsch H.-R. Petry 《The European Physical Journal A - Hadrons and Nuclei》2002,14(4):477-489
We compute electroweak form factors of the nucleon and photon transition form factors of non-strange baryon resonances up
to the third resonance region in a model with instanton-induced interaction. The calculation is based on the Bethe-Salpeter
equation for three light constituent quarks and is fully relativistic (U. L?ring et al., Eur. Phys. J. A 10, 309 (2001)). Static nucleon properties and photon resonance couplings are in good agreement with experiment and the Q2 behaviour of the experimentally known form factors up to large momentum transfer is accounted for.
Received: 4 April 2002 / Accepted: 2 May 2002 相似文献
2.
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
3.
E. Santopinto F. Iachello M.M. Giannini 《The European Physical Journal A - Hadrons and Nuclei》1998,1(3):307-315
We construct a simple 3-body quark model for the non strange nucleon resonances and we give results for the spectrum, the
helicity amplitudes and the transition form factors. All the observables, in particular the transition form factors, are evaluated
analytically and the results are compared with those of other models.
Received: 15 November 1997 相似文献
4.
T. Van Cauteren J. Ryckebusch B. Metsch H. -R. Petry 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):613-615
We present some of our results for the electromagnetic properties of excited Σ hyperons, computed within the framework of the Bonn constituent-quark model, which is based on the Bethe-Salpeter approach.
The seven parameters entering the model are fitted against the best-known baryon masses. Accordingly, the results for the
form factors and helicity amplitudes are genuine predictions. We compare with the scarce experimental data available and discuss
the processes in which Σ
*'s may play an important role. 相似文献
5.
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
6.
S. Migura D. Merten B. Metsch H. -R. Petry 《The European Physical Journal A - Hadrons and Nuclei》2006,28(1):41-53
We calculate mass spectra of charmed baryons within a relativistically covariant quark model based on the Bethe-Salpeter equation
in instantaneous approximation. Interactions are given by a linearly rising three-body confinement potential and a flavor-dependent
two-body force derived from QCD instanton effects. This model has already been successfully applied to the calculation of
light flavor baryon spectra and is now extended to heavy baryons. Within the same framework we compare the results to those
obtained with the more conventional one-gluon exchange potential. 相似文献
7.
We present results for the helicity amplitudes of the lowest-lying hyperon resonances Y*, computed within the framework of the Bonn Constituent-Quark model, which is based on the Bethe-Salpeter approach. The seven
parameters entering the model were fitted to the best-known baryon masses. Accordingly, the results for the helicity amplitudes
are genuine predictions. Some hyperon resonances are seen to couple more strongly to a virtual photon with finite Q2 than to a real photon. Other Y*'s, such as the S01(1670) Λ-resonance or the S11(1620) Σ-resonance, couple very strongly to real photons. We present a qualitative argument for predicting the behaviour of
the helicity asymmetries of baryon resonances at high Q2.-1 相似文献
8.
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
9.
10.
11.
U. Löring B.Ch. Metsch H.R. Petry 《The European Physical Journal A - Hadrons and Nuclei》2001,10(4):395-446
This is the second of a series of three papers treating light-baryon resonances up to 3 GeV within a relativistically covariant
quark model based on the three-fermion Bethe-Salpeter equation with instantaneous two- and three-body forces. In this paper
we apply the covariant Salpeter framework (which we developed in the first paper, U. L?ring, K. Kretzschmar, B.Ch. Metsch,
H.R. Petry, Eur. Phys. J. A 10, 309 (2001)) to specific quark model calculations. Quark confinement is realized by a linearly rising three-body string potential
with appropriate spinorial structures in Dirac space. To describe the hyperfine structure of the baryon spectrum we adopt
't Hooft's residual interaction based on QCD-instanton effects and demonstrate that the alternative one-gluon exchange is
disfavored on phenomenological grounds. Our fully relativistic framework allows to investigate the effects of the full Dirac
structures of residual and confinement forces on the structure of the mass spectrum. In the present paper we present a detailed
analysis of the complete non-strange-baryon spectrum and show that several prominent features of the nucleon spectrum such
as, e.g., the Roper resonance and approximate “parity doublets” can be uniformly explained due to a specific interplay of relativistic
effects, the confinement potential and 't Hooft's force. The results for the spectrum of strange baryons will be discussed
in a subsequent paper, see U. L?ring, B.Ch. Metsch, H.R. Petry, this issue, p. 447.
Received: 27 March 2001 / Accepted: 17 April 2001 相似文献
12.
13.
Form factors are calculated in the point form of relativistic quantum mechanics for the lowest energy states of a system made
of two scalar particles interacting via the exchange of a massless boson. They are compared to the exact results obtained
by using solutions of the Bethe-Salpeter equation which are well known in this case (Wick-Cutkosky model). The relevance of
the comparison is examined by considering other relativistic quantum-mechanics approaches where results are known or have
been obtained recently. Deficiencies of the point-form approach together with the single-particle current are emphasized.
They point to quite sizeable contributions of two-body currents. These ones are required to fulfil current conservation in
any case and to reproduce the high momentum transfer behaviour expected from the Born amplitude.
Received: 11 July 2001 / Accepted: 12 February 2002 相似文献
14.
Bo-Wen Xiao Xin Qian Bo-Qiang Ma 《The European Physical Journal A - Hadrons and Nuclei》2002,15(4):523-527
The electromagnetic form factor of the kaon meson is calculated in the light-cone formalism of the relativistic constituent
quark model. The calculated K+ form factor is consistent with almost all of the available experimental data at low-energy scale, while other properties
of the kaon could also be interrelated in this representation with reasonable parameters. Predictions of the form factors
for the charged and neutral kaons at a higher-energy scale are also given, and we find the non-zero K0 form factor at Q
2≠ 0 due to the mass difference between the strange and down quarks inside K0.
Received: 21 June 2002 / Accepted: 29 July 2002 / Published online: 3 December 2002
RID="a"
ID="a"e-mail: mabq@phy.pku.edu.cn
Communicated by A. Sch?fer 相似文献
15.
K. A. Aniol HAPPEX Collaboration 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):597-599
The HAPPEX Collaboration measured parity-violating electron scattering from
4He$(e, e)$and
H(e, e) in 2004 and 2005 for Q
2≤0.11GeV^2. Results for the strange-quark contributions to the electromagnetic form factors of the nucleon from the 2004 data
will be reviewed. Preliminary results from the 2005 data, which have significantly greater statistical precision, are G
E
s = 0.004±0.014stat±0.013syst for Q
2 = 0.0772GeV^2 from the helium data and G
E
s +0.088G
M
s = 0.004±0.011stat±0.005syst±0.004FF for Q
2 = 0.1089GeV^2 from the hydrogen data. 相似文献
16.
17.
S. Migura D. Merten B. Metsch H. -R. Petry 《The European Physical Journal A - Hadrons and Nuclei》2006,28(1):55-62
We calculate semileptonic decays of light and heavy baryons in a relativistically covariant constituent quark model. The model
is based on the Bethe-Salpeter equation in instantaneous approximation. It generates satisfactory mass spectra for mesons
and baryons up to the highest observable energies. Without introducing additional free parameters we compute on this basis
helicity amplitudes of electronic and muonic semileptonic decays of baryons. We thus obtain form factor ratios and decay rates
in good agreement with experiment. 相似文献
18.
C. Haupt B. Metsch H. -R. Petry 《The European Physical Journal A - Hadrons and Nuclei》2006,28(2):213-225
We show that static properties like the charge radius and the magnetic moment of relativistic three-fermion bound states with
instantaneous interactions can be formulated as expectation values with respect to intrinsically defined wave functions. The
resulting operators can be given a natural physical interpretation in accordance with relativistic covariance. We also indicate
how the formalism may be generalized to arbitrary moments. The method is applied to the computation of static baryon properties
with numerical results for the nucleon charge radii and the baryon octet magnetic moments. In addition, we make predictions
for the magnetic moments of some selected nucleon resonances and discuss the decomposition of the nucleon magnetic moments
in contributions of spin and angular momentum, as well as the evolution of these contributions with decreasing quark mass. 相似文献
19.
M. Koll R. Ricken D. Merten B.C. Metsch H.R. Petry 《The European Physical Journal A - Hadrons and Nuclei》2000,9(1):73-94
We present new results of a relativistic quark model based on the Bethe-Salpeter equation in its instantaneous approximation.
Assuming a linearly rising confinement potential with an appropriate spinorial structure in Dirac space and adopting a residual
interaction based on instanton effects, we can compute masses of the light mesons up to highest observed angular momenta with
a natural solution of the U
A(1) problem. The calculated ground states masses and the radial excitations describe the experimental results well. In this
paper, we will also discuss our results concerning numerous meson decay properties. For processes like π+/K
+↦e
+υeγ and 0-↦γγ at various photon virtualities, we find a good agreement with experimental data. We will also comment on the form factors
of the K
?3 decay and on the decay constants of the π, K and η mesons. For the sake of completeness, we will furthermore present the electromagnetic form factors of the charged π
and K mesons as well as a comparison of the radiative meson decay widths with the most recent experimental data.
Received: 28 August 2000 / Accepted: 12 September 2000 相似文献
20.
R. Bijker 《The European Physical Journal A - Hadrons and Nuclei》2007,32(4):403-407
The strange form factors of the nucleon are studied in a two-component model consisting of a three-quark intrinsic structure
surrounded by a meson cloud. A comparison with the available experimental world data from the SAMPLE, PVA4, HAPPEX and G0
Collaborations shows a good overall agreement. It is shown that the strangeness contribution to the electric and magnetic
form factors is of the order of a few percent. In particular, the strange quark contribution to the charge radius is small
〈r
2
s〉E = 0.005 fm^2 and to the magnetic moment it is positive μs = 0.315 μN . 相似文献