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1.
C. Hanhart 《Progress in Particle and Nuclear Physics》2003,50(2):227-234
A consistent counting scheme is presented that allows to study the reactions NN → NNπ within an effective field theory. Within this scheme the chiral expansion is shown to converge contrary to claims in the literature. 相似文献
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In recent years a two-scale expansion was established to study reactions of the type NN→NNπ within chiral perturbation theory. Then the diagrams of some subclasses that are invariant under the choice of the pion field no longer appear at the same chiral order. In this Letter we show that the proposed expansion still leads to well defined results. We also discuss the appropriate choice of the heavy baryon propagator. 相似文献
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A. E. Kudryavtsev V. E. Tarasov J. Haidenbauer C. Hanhart J. Speth 《Physics of Atomic Nuclei》2003,66(10):1946-1952
The reactions pp → dπ + η and pn → dπ 0 η are of special interest for investigating the a 0(980) (J P=0+) resonance in the process NN → da 0 → dπη. We study some aspects of those reactions within a general formalism and also in a concrete phenomenological model. In particular, it is shown that the presence of nonresonant (i.e., without excitation of the a 0 resonance) contributions to these reactions yields nonvanishing values for specific polarization observables, i.e., to effects like those generated by a 0 0 -f 0 mixing. An experimental determination of these observables for the reaction $\vec pp \to d\pi ^ + \eta $ would provide concrete information on the magnitude of those nonresonant contributions to πη production. We also discuss the possibility of extracting information about a 0 0 -f 0 mixing from the reaction $\vec pn \to d\pi ^0 \eta $ with a polarized proton beam. 相似文献
5.
The SELEX Collaboration has reported a very large isospin splitting of doubly charmed baryons. We show that this effect would imply that the doubly charmed baryons are very compact. One intriguing possibility is that such baryons have a linear geometry Q–q–Q where the light quark q oscillates between the two heavy quarks Q , analogous to a linear molecule such as carbon dioxide. However, using conventional arguments, the size of a heavy-light hadron is expected to be around 0.5 fm, much larger than the size needed to explain the observed large isospin splitting. Assuming the distance between two heavy quarks is much smaller than that between the light quark and a heavy one, the doubly heavy baryons are related to the heavy mesons via heavy quark–diquark symmetry. Based on this symmetry, we predict the isospin splittings for doubly heavy baryons including Ξcc, Ξbb and Ξbc. The prediction for the Ξcc is much smaller than the SELEX value. On the other hand, the Ξbb baryons are predicted to have an isospin splitting as large as (6.3±1.7) MeV. An experimental study of doubly bottomed baryons is therefore very important to better understand the structure of baryons with heavy quarks. 相似文献
6.
S. Capstick A. Švarc L. Tiator J. Gegelia M. M. Giannini E. Santopinto C. Hanhart S. Scherer T. -S. H. Lee T. Sato N. Suzuki 《The European Physical Journal A - Hadrons and Nuclei》2008,35(3):253-266
The physical meaning of bare and dressed scattering matrix singularities has been investigated. Special attention has been
attributed to the role of the well-known invariance of the scattering matrix with respect to the field transformation of the
effective Lagrangian. Examples of evaluating bare and dressed quantities in various models are given. 相似文献
7.
L. Roca C. Hanhart E. Oset U. -G. Meißner 《The European Physical Journal A - Hadrons and Nuclei》2006,27(3):373-380
The Λ(1520)-resonance has been recently studied in a unitarized coupled-channel formalism with πΣ(1385), KΞ(1530), ˉN and πΣ as constituents blocks. We provide a theoretical study of the predictions of this model in physical observables of
the pp → pK+K-p and pp → pK+π0π0Λ reactions. In particular, we show that the ratio between the π0π0Λ and K-p mass distributions can provide valuable information on the ratio of the couplings of the Λ(1520)-resonance to πΣ(1385) and
ˉN than the theory predicts. Calculations are done for energies which are accessible in an experimental facility like COSY at
Jülich or the developing CSR facility at Lanzhou. 相似文献
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The analytic properties of scattering amplitudes provide a meeting point for experimental and theoretical investigations of baryon resonances. Pole positions and residues allow for a parameterization of resonances in a well-defined way which relates different reactions. The recent progress made within the Jiilich model is summarized. 相似文献
10.
The role of the background in the extraction of resonance contributions from meson–baryon scattering
The separation of background and resonance contributions in pion–nucleon scattering is an often discussed issue. We investigate to what extent the background can be separated from the pole contribution. For illustration we use results from an analytic model for the meson–baryon interaction derived from meson exchange. We focus on the two distinct cases of an elastic and a highly inelastic resonance, namely the Δ(1232) and the Δ∗(1700). Our results are also relevant for studies of dynamically generated resonances and attempts to extract bare quantities from hadronic models to be compared to quark model results. 相似文献