Resonance Dynamics in Coupled Channels

Döring, Michael

doi:10.1142/s2010194514600544

Cited by 10 publications

(12 citation statements)

References 39 publications

(30 reference statements)

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“…• Of the three spectral features that emerge in this channel, two are associated with the Roper resonance. [This two-pole character of the Roper is common to many analyses of the scattering data, including one involving Roper himself (Arndt et al, 1985) and more recent analyses of πN scattering data (Arndt et al, 2006;Cutkosky and Wang, 1990;Döring et al, 2009). ]…”

Section: Dynamical Coupled Channels Calculationsmentioning

confidence: 86%

Colloquium : Roper resonance: Toward a solution to the fifty year puzzle

2019

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For half a century, the Roper resonance has defied understanding. Discovered in 1963, it appears to be an exact copy of the proton except that its mass is 50% greater. The mass is the first problem: it is difficult to explain with any theoretical tool that can validly be used to study the strong-interaction piece of the Standard Model of Particle Physics, i.e. quantum chromodynamics [QCD]. In the last decade, a new challenge has appeared, viz. precise information on the proton-to-Roper electroproduction transition form factors, reaching out to momentum transfer Q 2 ≈ 4.5 GeV 2 . This scale probes the domain within which hard valence-quark degrees-of-freedom could be expected to determine form factor behavior. Hence, with this new data the Roper resonance becomes a problem for strong-QCD [sQCD]. An explanation of how and where the Roper resonance fits into the emerging spectrum of hadrons cannot rest on a description of its mass alone. Instead, it must combine an understanding of the Roper's mass and width with a detailed account of its structure and how that structure is revealed in the momentum dependence of the transition form factors. Furthermore, it must unify all this with a similarly complete picture of the proton from which the Roper resonance is produced. This is a prodigious task, but a ten-year international collaborative effort, drawing together experimentalists and theorists, has presented a solution to the puzzle. Namely, the observed Roper is at heart the proton's first radial excitation, consisting of a dressedquark core augmented by a meson cloud that reduces the core mass by approximately 20% and materially alters its electroproduction form factors on Q 2 < 2 m 2 N , where m N is the proton's mass. We describe the experimental motivations and developments which enabled electroproduction data to be procured within a domain that is unambiguously the purview of sQCD, thereby providing a real challenge and opportunity for modern theory; and survey the developments in reaction models and QCD theory that have enabled this conclusion to be drawn about the nature of the Roper resonance.

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Section: Dynamical Coupled Channels Calculationsmentioning

confidence: 86%

Colloquium : Roper resonance: Toward a solution to the fifty year puzzle

2019

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“…1 should yield masses that are larger than experiment because, as explained elsewhere [10,77], the kernel in Fig. 1 omits all those resonant contributions which may be associated with the meson-baryon final-state interactions that are resummed in dynamical coupled channels models [78][79][80] in order to transform a bare-baryon into the observed state. Our Faddeev equation should therefore be understood as producing the dressed-quark core of the bound-state, not the completely-dressed and hence observable object.…”

Section: Results From the Faddeev Equationsmentioning

confidence: 99%

Contact-interaction Faddeev equation and,inter alia, proton tensor charges

Chen

Cloët

et al. 2015

Phys. Rev. D

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A confining, symmetry-preserving, Dyson-Schwinger equation treatment of a vector ⊗ vector contact interaction is used to formulate Faddeev equations for the nucleon and ∆-baryon in which the kernel involves dynamical dressed-quark exchange and whose solutions therefore provide momentumdependent Faddeev amplitudes. These solutions are compared with those obtained in the static approximation and with a QCD-kindred formulation of the Faddeev kernel. They are also used to compute a range of nucleon properties, amongst them: the proton's σ-term; the large Bjorken-x values of separate ratios of unpolarised and longitudinally-polarised valence u-and d-quark parton distribution functions; and the proton's tensor charges, which enable one to directly determine the effect of dressed-quark electric dipole moments (EDMs) on neutron and proton EDMs.

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“…They differ at first glance, but the discrepancies can be well understood: The solutions of the Faddeev equation with the kernel in Fig. 1 should be interpreted as the dressed-quark core of the bound-state, instead of representing the fully-dressed observable object, because the kernel omits [29,30] all those resonant contributions which may be associated with the meson-baryoncloud finite-state-interactions (MB FSIs) resummed in DCC models [28,[31][32][33][34][35][36]. Therefore, the critical comparison is not between the computed dressed-quark core masses and empirical values of the pole-positions but between the former and the values determined for the mesonundressed bare bound-state; e.g.…”

Section: Nucleon and Roper Structurementioning

confidence: 99%

Form factors for the Nucleon-to-Roper electromagnetic transition at large-Q²

et al. 2020

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We report on a recent calculation of all Roper-related electromagnetic transtions form factors, cov ering the range of energies that next-to-come planned experiments are expected to map. Direct reliable cal culations were performed, within a Poincaré covariant approach of the three-body bound-state problem, up to Q2/m2N=6; approximated then by applying the Schlessinger point method and the results eventually extended up to Q2/m2N ≃12 via analytic continuation.

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Resonance Dynamics in Coupled Channels

Cited by 10 publications

References 39 publications

Colloquium : Roper resonance: Toward a solution to the fifty year puzzle

Colloquium : Roper resonance: Toward a solution to the fifty year puzzle

Contact-interaction Faddeev equation and,inter alia, proton tensor charges

Form factors for the Nucleon-to-Roper electromagnetic transition at large-Q²

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Resonance Dynamics in Coupled Channels

Cited by 10 publications

References 39 publications

Colloquium : Roper resonance: Toward a solution to the fifty year puzzle

Colloquium : Roper resonance: Toward a solution to the fifty year puzzle

Contact-interaction Faddeev equation and,inter alia, proton tensor charges

Form factors for the Nucleon-to-Roper electromagnetic transition at large-Q2

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Form factors for the Nucleon-to-Roper electromagnetic transition at large-Q²