Nuclear Pion Photoproduction

Nagl, A.; Devanathan, V.; Überall, H.

doi:10.1007/bfb0048454

Cited by 15 publications

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“…An early nonrelativistic study by Bennhold and Tanabe of the coherent η photoproduction process predicted 4 He to have the largest cross section of the three nuclei 4 He, 12 C, and 40 Ca [1]. A recent nonrelativistic study of this process seems to confirm this earlier prediction, although important quantitative differences do emerge [3].…”

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confidence: 82%

“…This is in contrast to nonrelativistic treatments that, instead, use the vector density [1,2,[10][11][12]. The tensor density is a manifestation of the relativistic character of this approach.…”

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confidence: 98%

“…This "M ⋆ effect" is a direct consequence of the enhancement of the lower component of the Dirac spinor-which is determined dynamically, rather than from a free-space relation. Moreover, there is an additional relativistic contribution for open-shell nuclei, such as 12 C; note that we are treating 12 C as a closed p 3/2 but open p 1/2 orbital. This can be most easily seen by assuming a free-space relation between the upper and lower components of the Dirac spinors.…”

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confidence: 99%

“…The form of the elementary amplitude used here is standard but not unique. There are many other choices which are equivalent on-shell, but can give vastly different results off-shell [6,12]. Although there are some attempts to deal with this issue [3], a detailed microscopic model is needed to take the amplitude off-shell.…”

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confidence: 99%

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Nuclear dependence of the coherentηphotoproduction reaction in a relativistic approach

et al. 1998

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We study the nuclear (or A) dependence of the coherent η photoproduction reaction in a relativistic impulse approximation approach. We use a standard relativistic parameterization of the elementary amplitude, based on a set of four Lorentz-and gauge-invariant amplitudes, to calculate the coherent production cross section from 4 He, 12 C, and 40 Ca. In contrast to nonrelativistic treatments, our approach maintains the full relativistic structure of the process. The nuclear structure affects the process through the ground-state tensor density. This density is sensitive to relativistic effects and depends on A in a different manner than the vector density used in nonrelativistic approaches. This peculiar dependence results in 4 He having a cross section significantly smaller than that of 12 Cin contrast to existent nonrelativistic calculations. Distortion effects are incorporated through an η-nucleus optical potential that is computed in a simple "tρ" approximation. The nuclear dependence of the coherent η photoproduction process offers a unique opportunity to investigate medium modifications to the elementary γN → ηN amplitude and might help distinguish between different theoretical models that provide an equally good description of the elementary process. In particular, the role played by the background is very significant in spin-isospin saturated nuclei where the dominant resonance S 11 (1535) is suppressed. Furthermore, this reaction contributes significantly to our understanding of nucleon-resonance formation and sheds some light on the propagation of these resonances through the nuclear medium. The A dependence of this reaction is affected by the propagation of the produced η-meson through its interaction with the nucleus. Moreover, the coherent process is sensitive to the whole nuclear volume and, thus, depends on bulk properties of the nucleus. While nonrelativistic treatments suggest that nuclear-structure effects manifest themselves through the conserved vector (or baryon) density [1-3], our recent relativistic analysis suggests that, rather, it is the tensor density that affects the process [4]. This represents an important result, since the tensor density-a quantity as fundamental as the vector density-is not well determined by experiment.An early nonrelativistic study by Bennhold and Tanabe of the coherent η photoproduction process predicted 4 He to have the largest cross section of the three nuclei 4 He, 12 C, and 40 Ca [1]. A recent nonrelativistic study of this process seems to confirm this earlier prediction, although important quantitative differences do emerge [3]. In nonrelativistic treatments the coherent cross section is proportional to the square of the Fourier transform of the vector density. Thus, the particular A dependence predicted by these calculations emerges from a competition between A, which tends to increase the cross section for larger nuclei, and the vector form-factor-which falls rapidly with A. This competition results in 4 He having the largest cross section. Theoretical stud...

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confidence: 82%

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confidence: 98%

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confidence: 99%

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confidence: 99%

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Nuclear dependence of the coherentηphotoproduction reaction in a relativistic approach

et al. 1998

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“…[13]. In the earlier treatments [9,10,11,12], these parameters were determined initially from a phase shift analysis performed by Rowe, Salomon, and Landau [14], but then were modified to obtain the best fit for the π-nucleus scattering and pionic atom data.…”

Section: Derivation Of the Optical Potentialmentioning

confidence: 99%

Pion-nucleus optical potential valid up to the Δ-resonance region

Abu‐Raddad

2002

Phys. Rev. C

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We present in this article an optical potential for the π-nucleus interaction that can be used in various studies involving π-nucleus channels. Based on earlier treatments of the low energy π-nucleus optical potential, we have derived a potential expression applicable from threshold up to the ∆-resonance region. We extracted the impulse approximation form for this potential from the π − N scattering amplitude and then added to it kinematical and physical corrections. The kinematic corrections arise from transforming the impulse approximation expression from the π−N center of mass frame to the π-nucleus center of mass frame, while the physical corrections arise mostly from the many-body nature of the π-nucleus interaction. By taking advantage of the experimental progress in our knowledge of the π − N process, we have updated earlier treatments with parameters calculated from state-of-the-art experimental measurements.

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The structure of the world from pure numbers

Tipler¹

2005

Rep. Prog. Phys.

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I argue that the (extended) Standard Model (SM) of particle physics and the renormalizable Feynman-Weinberg theory of quantum gravity comprise a theory of everything. I show that imposing the appropriate cosmological boundary conditions make the theory finite. The infinities that are normally renormalized away and the series divergence infinities are both eliminated by the same mechanism. Furthermore, this theory can resolve the horizon, flatness, and isotropy problems of cosmology. Joint mathematical consistency naturally yields a scale-free, Gaussian, adiabatic perturbation spectrum, and more matter than antimatter. I show that mathematical consistency of the theory requires the universe to begin at an initial singularity with a pure SU (2) L gauge field. I show that quantum mechanics requires this field to have a Planckian spectrum whatever its temperature. If this field has managed to survive thermalization to the present day, then it would be the CMBR. If so, then we would have a natural explanation for the dark matter and the dark energy. I show that isotropic ultrahigh energy (UHE) cosmic rays are explained if the CMBR is a pure SU (2) L gauge field. The SU (2) L nature of the CMBR may have been seen in the Sunyaev-Zel'dovich effect. I propose several simple experiments to test the hypothesis.KEY WORDS: Axiom of Choice, Axiom of Constructibility, Power Set Axiom, Large Cardinal Axioms, Continuum Hypothesis, Generalized Continuum Hypothesis, dark matter, dark energy, cosmological constant, flatness problem, isotropy problem, horizon problem, Harrison-Zel'dovich spectrum, quantum cosmology, UHE cosmic rays, varying constants, curvature singularities, singularity hypostases, finite quantum gravity, gauge hierarchy problem, strong CP problem, triviality, black hole information problem, event horizons, holography, Sunyaev-Zel'dovich effect, CMBR, Penning Traps 1 arXiv:0704.3276v1 [hep-th]

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Nuclear Pion Photoproduction

Cited by 15 publications

References 0 publications

Nuclear dependence of the coherentηphotoproduction reaction in a relativistic approach

Nuclear dependence of the coherentηphotoproduction reaction in a relativistic approach

Pion-nucleus optical potential valid up to the Δ-resonance region

The structure of the world from pure numbers

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