On the basis of the three-particle Bethe-Salpeter equation we formulated a relativistic quark mod... more On the basis of the three-particle Bethe-Salpeter equation we formulated a relativistic quark model for baryons. Assuming the propagators to be given by their free form with constituent quark masses and the interaction kernel by an instantaneous potential, which contains a string-like parameterization of confinement and a flavor dependent interaction motivated by instanton effects we can account for the major features in the baryon spectrum, such as the low position of the Roper resonance and the occurrence of approximate parity doublets apparent in the N-and Λ-spectra.
We consider the existence of bound systems consisting of two quarks and two antiquarks (q^2\bar q... more We consider the existence of bound systems consisting of two quarks and two antiquarks (q^2\bar q^2) within the framework of a constituent quark model. The underlying quark dynamics is described by a linear confinement potential and an effective q^2\bar q^2 interaction which has its origin in instanton effects of QCD. We calculate the spectra and examine the internal structure of the states found
We present a covariant scheme to calculate mesonic transitions in the framework of the Salpeter e... more We present a covariant scheme to calculate mesonic transitions in the framework of the Salpeter equation for q¯q-states. The full Bethe Salpeter amplitudes are reconstructed from equal time amplitudes which were obtained in a previous paper [1] by solving the Salpeter equation for a confining plus an instanton induced interaction. This method is applied to calculate electromagnetic form factors and decay widths of low lying pseudoscalar and vector mesons including predictions for CEBAF experiments. We also describe the momentum transfer dependence for the processes π 0,η,η ′ → γγ ∗. Typeset using REVTEX 1 I.
Within the language of quark-gluon and Reggeon exchanges it is possible to relate the total cross... more Within the language of quark-gluon and Reggeon exchanges it is possible to relate the total cross section and the production suppression parameter for particles with different flavors to the masses of dressed quarks. We calculated the quenching of the suppression ...
The spectrum of Ni V has been measured in the region from approximately 300 A to 450 A where the ... more The spectrum of Ni V has been measured in the region from approximately 300 A to 450 A where the transitions between the 3d6-3d54p configurations have been located. Out of the 34 theoretically possible levels of the 3d 6 configuration 33 levels have been determined, only the higher 1S o level is missing. Out of the 214 levels of the 3d54p configuration 177 levels are known. All these level values and the classified lines are tabulated at the end of this paper. Parametric (configuration) calculations of the levels of the 3d 6 and 3d54p configurations have been made.
Following the recent discovery of a very strong magnetic dipole transition in 48Ca to a state a't... more Following the recent discovery of a very strong magnetic dipole transition in 48Ca to a state a't 10.23 MeV in high-resolution inelastic electron scattering, results of a detailed search for M 1 strength in the other N = 28 Isotones S°Ti, S;Cr and 54 Fe are described. The M 1 strength found in the investigated region of excitation energy E x ~ 7-12 MeV is very fragmented and considerably quenched in comparison to predictions of shell model calculations in a model space that includes up to 2p-2h excitations.
We investigate the structure of the instantaneous Bethe-Salpeter equation for qq-bound states in ... more We investigate the structure of the instantaneous Bethe-Salpeter equation for qq-bound states in the general case of unequal quark masses and develop a numerical scheme for the calculation of mass spectra and Bethe-Salpeter amplitudes. In order to appreciate the merits of the various competing models beyond the reproduction of the mass spectra we present explicit formulas to calculate electroweak decays. The results for an explicit quark model will be compared to experimental data in a subsequent paper [1].
ABSTRACT It is pointed out that the existence of similar collective band structure fostered on th... more ABSTRACT It is pointed out that the existence of similar collective band structure fostered on the excited J = 1/2 states is a systematic feature of the nonstrange and strange baryon resonances.
Predictions for the electromagnetic form factors of the Λ, Σ and Ξ hyperons are presented. The nu... more Predictions for the electromagnetic form factors of the Λ, Σ and Ξ hyperons are presented. The numerical calculations are performed within the framework of the fully relativistic constituent-quark model developed by the Bonn group. The computed magnetic moments compare favorably with the experimentally known values. Most magnetic form factors GM (Q 2) can be parametrized in terms of a dipole with cutoff masses ranging from 0.79 to 1.14 GeV.
Within the framework of the instantaneous Bethe-Salpeter equation, we present a detailed analysis... more Within the framework of the instantaneous Bethe-Salpeter equation, we present a detailed analysis of light meson spectra with respect to various parameterizations of confinement in Dirac space. Assuming a linearly rising quark-antiquark potential, we investigate two different spinorial forms (Dirac structures), namely 1 2 (1 I⊗1 I−γ 0 ⊗γ 0) as well as the UA(1)-invariant combination 1 2 (1 I⊗1 I−γ 5 ⊗ γ 5 − γ µ ⊗ γµ), both providing a good description of the ground state Regge trajectories up to highest observed angular momenta. Whereas the first structure is slightly prefered concerning numerous meson decay properties (see [41]), we find the UA(1)-invariant force to be much more appropriate for the description of a multitude of higher mass resonances discovered in the data of the Crystal Barrel collaboration during the last few years. Furthermore, this confinement structure has the remarkable feature to yield a linear dependence of masses on their radial excitation number. For many experimental resonances such a trajectory-like behaviour was observed by Anisovich et al. We can confirm that almost the same slope occurs for all trajectories. Adding the UA(1)-breaking instanton induced 't Hooft interaction we can compute the pseudoscalar mass splittings with both Dirac structures and for the scalar mesons a natural mechanism of flavour mixing is achieved. In the scalar sector, the two models provide completely different ground state and excitation masses, thus leading to different assignments of possibleqq states in this region. The scalar meson masses calculated with the structure 1 2 (1 I ⊗ 1 I − γ 5 ⊗ γ 5 − γ µ ⊗ γµ) are in excellent agreement with the K-matrix poles deduced from experiment by Anisovich and coworkers.
This is the second of a series of three papers treating light baryon resonances up to 3 GeV withi... more 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 [1]) 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 QCDinstanton effects and demonstrate that the alternative one-gluon-exchange is disfavored 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 [2].
The spectra and electroweak decay properties of light mesons are analyzed within the framework of... more The spectra and electroweak decay properties of light mesons are analyzed within the framework of the instantaneous Bethe-Salpeter equation. The interaction kernel comprises alternative spin-structures for a parameterization of confinement and a residual quark-antiquark interaction based on instanton effects. It is shown that only with a vector confinement the parameters can be chosen such as to yield an excellent description of the light pseudoscalar and vector mesons including weak and two photon decays. However it is found that it is not possible to reconcile this with the Regge behavior of higher lying meson states with the same parameter set.
We consider the existence of bound systems consisting of two quarks and two antiquarks (q2q̄2) wi... more We consider the existence of bound systems consisting of two quarks and two antiquarks (q2q̄2) within the framework of a constituent quark model. The underlying quark dynamics is described by a linear confinement potential and an effective q2q̄2 interaction which has its origin in instanton effects of QCD. We calculate the spectra and examine the internal structure of the states found.
The strength functions for the β+ decay of the proton rich nuclei 34Ar and 35Ar into a Gamow Tell... more The strength functions for the β+ decay of the proton rich nuclei 34Ar and 35Ar into a Gamow Teller resonance are studied using shell model wave functions. A resonance-like structure is calculated to be positioned about 3 MeV above the state that is the isobaric analogue state of the ground state of the decaying nucleus. Similarly to previous calculations for A = 32 and 36 these nuclei posses a spin-flip resonance based on the excited counterpart of the ground state.
Contemporary Topics in Medium Energy Physics, 1994
Our present understanding of hadronic matter is obscured by the confinement problem; the fundamen... more Our present understanding of hadronic matter is obscured by the confinement problem; the fundamental constituents of hadrons should never appear as observable states and hence a relativistic theory of bound states must in principle stand at the beginning of any computation of hadronic reactions. The problem of formulating such a theory is by no means particular to QCD. So far, even for simpler field theories no practicable theory has been developed. By exploiting the fact that QCD is a gauge theory, the bound state problem of QCD can be studied by lattice calculations, but it is still questionable whether the extremely rich spectrum of mesons and baryons will be fmally obtained. At the moment, the link between QCD and low-energy hadron physics is given by phenomenological models only, and very few genuine QCD results enter in the corresponding model assumptions. In this contribution, we want to stress the possible role of an instanton induced quark force, both in hadron spectroscopy and intermediate energy nuclear physics. This solves none of the fundamental problems related to confinement, but seems to be an excellent candidate to produce the correct mass splitting in the observed resonance spectrum, once we have fixed an admittedly phenomenological confinement prescription; in particular, they help to understand the role of chiral invariance in quark models in a consistent way.
On the basis of the three-particle Bethe-Salpeter equation we formulated a relativistic quark mod... more On the basis of the three-particle Bethe-Salpeter equation we formulated a relativistic quark model for baryons. Assuming the propagators to be given by their free form with constituent quark masses and the interaction kernel by an instantaneous potential, which contains a string-like parameterization of confinement and a flavor dependent interaction motivated by instanton effects we can account for the major features in the baryon spectrum, such as the low position of the Roper resonance and the occurrence of approximate parity doublets apparent in the N-and Λ-spectra.
We consider the existence of bound systems consisting of two quarks and two antiquarks (q^2\bar q... more We consider the existence of bound systems consisting of two quarks and two antiquarks (q^2\bar q^2) within the framework of a constituent quark model. The underlying quark dynamics is described by a linear confinement potential and an effective q^2\bar q^2 interaction which has its origin in instanton effects of QCD. We calculate the spectra and examine the internal structure of the states found
We present a covariant scheme to calculate mesonic transitions in the framework of the Salpeter e... more We present a covariant scheme to calculate mesonic transitions in the framework of the Salpeter equation for q¯q-states. The full Bethe Salpeter amplitudes are reconstructed from equal time amplitudes which were obtained in a previous paper [1] by solving the Salpeter equation for a confining plus an instanton induced interaction. This method is applied to calculate electromagnetic form factors and decay widths of low lying pseudoscalar and vector mesons including predictions for CEBAF experiments. We also describe the momentum transfer dependence for the processes π 0,η,η ′ → γγ ∗. Typeset using REVTEX 1 I.
Within the language of quark-gluon and Reggeon exchanges it is possible to relate the total cross... more Within the language of quark-gluon and Reggeon exchanges it is possible to relate the total cross section and the production suppression parameter for particles with different flavors to the masses of dressed quarks. We calculated the quenching of the suppression ...
The spectrum of Ni V has been measured in the region from approximately 300 A to 450 A where the ... more The spectrum of Ni V has been measured in the region from approximately 300 A to 450 A where the transitions between the 3d6-3d54p configurations have been located. Out of the 34 theoretically possible levels of the 3d 6 configuration 33 levels have been determined, only the higher 1S o level is missing. Out of the 214 levels of the 3d54p configuration 177 levels are known. All these level values and the classified lines are tabulated at the end of this paper. Parametric (configuration) calculations of the levels of the 3d 6 and 3d54p configurations have been made.
Following the recent discovery of a very strong magnetic dipole transition in 48Ca to a state a't... more Following the recent discovery of a very strong magnetic dipole transition in 48Ca to a state a't 10.23 MeV in high-resolution inelastic electron scattering, results of a detailed search for M 1 strength in the other N = 28 Isotones S°Ti, S;Cr and 54 Fe are described. The M 1 strength found in the investigated region of excitation energy E x ~ 7-12 MeV is very fragmented and considerably quenched in comparison to predictions of shell model calculations in a model space that includes up to 2p-2h excitations.
We investigate the structure of the instantaneous Bethe-Salpeter equation for qq-bound states in ... more We investigate the structure of the instantaneous Bethe-Salpeter equation for qq-bound states in the general case of unequal quark masses and develop a numerical scheme for the calculation of mass spectra and Bethe-Salpeter amplitudes. In order to appreciate the merits of the various competing models beyond the reproduction of the mass spectra we present explicit formulas to calculate electroweak decays. The results for an explicit quark model will be compared to experimental data in a subsequent paper [1].
ABSTRACT It is pointed out that the existence of similar collective band structure fostered on th... more ABSTRACT It is pointed out that the existence of similar collective band structure fostered on the excited J = 1/2 states is a systematic feature of the nonstrange and strange baryon resonances.
Predictions for the electromagnetic form factors of the Λ, Σ and Ξ hyperons are presented. The nu... more Predictions for the electromagnetic form factors of the Λ, Σ and Ξ hyperons are presented. The numerical calculations are performed within the framework of the fully relativistic constituent-quark model developed by the Bonn group. The computed magnetic moments compare favorably with the experimentally known values. Most magnetic form factors GM (Q 2) can be parametrized in terms of a dipole with cutoff masses ranging from 0.79 to 1.14 GeV.
Within the framework of the instantaneous Bethe-Salpeter equation, we present a detailed analysis... more Within the framework of the instantaneous Bethe-Salpeter equation, we present a detailed analysis of light meson spectra with respect to various parameterizations of confinement in Dirac space. Assuming a linearly rising quark-antiquark potential, we investigate two different spinorial forms (Dirac structures), namely 1 2 (1 I⊗1 I−γ 0 ⊗γ 0) as well as the UA(1)-invariant combination 1 2 (1 I⊗1 I−γ 5 ⊗ γ 5 − γ µ ⊗ γµ), both providing a good description of the ground state Regge trajectories up to highest observed angular momenta. Whereas the first structure is slightly prefered concerning numerous meson decay properties (see [41]), we find the UA(1)-invariant force to be much more appropriate for the description of a multitude of higher mass resonances discovered in the data of the Crystal Barrel collaboration during the last few years. Furthermore, this confinement structure has the remarkable feature to yield a linear dependence of masses on their radial excitation number. For many experimental resonances such a trajectory-like behaviour was observed by Anisovich et al. We can confirm that almost the same slope occurs for all trajectories. Adding the UA(1)-breaking instanton induced 't Hooft interaction we can compute the pseudoscalar mass splittings with both Dirac structures and for the scalar mesons a natural mechanism of flavour mixing is achieved. In the scalar sector, the two models provide completely different ground state and excitation masses, thus leading to different assignments of possibleqq states in this region. The scalar meson masses calculated with the structure 1 2 (1 I ⊗ 1 I − γ 5 ⊗ γ 5 − γ µ ⊗ γµ) are in excellent agreement with the K-matrix poles deduced from experiment by Anisovich and coworkers.
This is the second of a series of three papers treating light baryon resonances up to 3 GeV withi... more 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 [1]) 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 QCDinstanton effects and demonstrate that the alternative one-gluon-exchange is disfavored 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 [2].
The spectra and electroweak decay properties of light mesons are analyzed within the framework of... more The spectra and electroweak decay properties of light mesons are analyzed within the framework of the instantaneous Bethe-Salpeter equation. The interaction kernel comprises alternative spin-structures for a parameterization of confinement and a residual quark-antiquark interaction based on instanton effects. It is shown that only with a vector confinement the parameters can be chosen such as to yield an excellent description of the light pseudoscalar and vector mesons including weak and two photon decays. However it is found that it is not possible to reconcile this with the Regge behavior of higher lying meson states with the same parameter set.
We consider the existence of bound systems consisting of two quarks and two antiquarks (q2q̄2) wi... more We consider the existence of bound systems consisting of two quarks and two antiquarks (q2q̄2) within the framework of a constituent quark model. The underlying quark dynamics is described by a linear confinement potential and an effective q2q̄2 interaction which has its origin in instanton effects of QCD. We calculate the spectra and examine the internal structure of the states found.
The strength functions for the β+ decay of the proton rich nuclei 34Ar and 35Ar into a Gamow Tell... more The strength functions for the β+ decay of the proton rich nuclei 34Ar and 35Ar into a Gamow Teller resonance are studied using shell model wave functions. A resonance-like structure is calculated to be positioned about 3 MeV above the state that is the isobaric analogue state of the ground state of the decaying nucleus. Similarly to previous calculations for A = 32 and 36 these nuclei posses a spin-flip resonance based on the excited counterpart of the ground state.
Contemporary Topics in Medium Energy Physics, 1994
Our present understanding of hadronic matter is obscured by the confinement problem; the fundamen... more Our present understanding of hadronic matter is obscured by the confinement problem; the fundamental constituents of hadrons should never appear as observable states and hence a relativistic theory of bound states must in principle stand at the beginning of any computation of hadronic reactions. The problem of formulating such a theory is by no means particular to QCD. So far, even for simpler field theories no practicable theory has been developed. By exploiting the fact that QCD is a gauge theory, the bound state problem of QCD can be studied by lattice calculations, but it is still questionable whether the extremely rich spectrum of mesons and baryons will be fmally obtained. At the moment, the link between QCD and low-energy hadron physics is given by phenomenological models only, and very few genuine QCD results enter in the corresponding model assumptions. In this contribution, we want to stress the possible role of an instanton induced quark force, both in hadron spectroscopy and intermediate energy nuclear physics. This solves none of the fundamental problems related to confinement, but seems to be an excellent candidate to produce the correct mass splitting in the observed resonance spectrum, once we have fixed an admittedly phenomenological confinement prescription; in particular, they help to understand the role of chiral invariance in quark models in a consistent way.
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Papers by B. Metsch