Analysis of pion photoproduction data

Arndt, Richard A.; Briscoe, W. J.; Strakovsky, I. I.; Workman, R. L.

doi:10.1103/physrevc.66.055213

Cited by 254 publications

(417 citation statements)

References 59 publications

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“…The value of s 0 1.2 GeV 2 was found in Ref. [40] from the description of the pion photoproduction multipole amplitudes [51,52]. With this value of s 0 , we obtained a good description of π electroproduction data at Q 2 = 0.4 and 0.65 GeV 2 in the first, second, and third resonance regions [41,42].…”

Section: B Unitary Isobar Modelsupporting

confidence: 51%

“…The quantities labeled by tildes (M,˜ ,β πN ) correspond to the values used in the analysis and in the extraction of the γ * p → N * helicity amplitudes. W dependence of M 3/2 1+ remains unchanged and close to that from the GWU analysis [52] at Q 2 = 0, if the same normalizations of the amplitudes at the resonance position are used. This constraint on the large M 3/2 1+ amplitude plays an important role in the reliable extraction of the amplitudes for the γ * N → (1232)P 33 transition.…”

Section: Resonance Contributionsmentioning

confidence: 59%

See 1 more Smart Citation

Electroexcitation of nucleon resonances from CLAS data on single pion electroproduction

Aznauryan¹,

Burkert²,

Biselli³

et al. 2009

Phys. Rev. C

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252

380

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We present results on the electroexcitation of the low mass resonances (1232)P 33 , N (1440)P 11 , N (1520)D 13 , and N (1535)S 11 in a wide range of Q 2 . The results were obtained in the comprehensive analysis of data from the Continuous Electron Beam Accelerator Facility (CEBAF) large acceptance spectrometer (CLAS) detector at the Thomas Jefferson National Accelerator Facility (JLab) on differential cross sections, longitudinally polarized beam asymmetries, and longitudinal target and beam-target asymmetries for π electroproduction off the proton. The data were analyzed using two conceptually different approaches-fixed-t dispersion relations and a unitary isobar model-allowing us to draw conclusions on the model sensitivity of the obtained electrocoupling amplitudes. The amplitudes for the (1232)P 33 show the importance of a meson-cloud contribution to quantitatively explain the magnetic dipole strength, as well as the electric and scalar quadrupole transitions. They do not show any tendency of approaching the pQCD regime for Q 2 6 GeV 2 . For the Roper resonance, N (1440)P 11 , the data provide strong evidence that this state is a predominantly radial excitation of a three-quark (3q) ground state. Measured in pion electroproduction, the transverse helicity amplitude for the N (1535)S 11 allowed us to obtain the branching ratios of this state to the πN and ηN channels via comparison with the results extracted from η electroproduction. The extensive CLAS data also enabled the extraction of the γ * p → N (1520)D 13 and N (1535)S 11 longitudinal helicity amplitudes with good precision. For the N (1535)S 11 , these results became a challenge for quark models and may be indicative of large meson-cloud contributions or of representations of this state that differ from a 3q excitation. The transverse amplitudes for the N (1520)D 13 clearly show the rapid changeover from helicity-3/2 dominance at the real photon point to helicity-1/2 dominance at Q 2 > 1 GeV 2 , confirming a long-standing prediction of the constituent quark model.

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Section: B Unitary Isobar Modelsupporting

confidence: 51%

Section: Resonance Contributionsmentioning

confidence: 59%

Electroexcitation of nucleon resonances from CLAS data on single pion electroproduction

Aznauryan¹,

Burkert²,

Biselli³

et al. 2009

Phys. Rev. C

Self Cite

252

380

View full text Add to dashboard Cite

show abstract

“…2.1) by fitting to the electroproduction data. Also based on different K-matrix approximations but including a larger number of channels are for example the SAID parametrization [59,60], the KSU model [61,62], the Giessen coupled-channel approach [63][64][65][66] and the Bonn-Gatchina model [67][68][69].…”

Section: Helicity Amplitudes Vs Transition Form Factorsmentioning

confidence: 99%

Baryons as relativistic three-quark bound states

Eichmann

Sanchis-Alepuz

Williams

et al. 2016

Progress in Particle and Nuclear Physics

436

530

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We review the spectrum and electromagnetic properties of baryons described as relativistic three-quark bound states within QCD. The composite nature of baryons results in a rich excitation spectrum, whilst leading to highly non-trivial structural properties explored by the coupling to external (electromagnetic and other) currents. Both present many unsolved problems despite decades of experimental and theoretical research. We discuss the progress in these fields from a theoretical perspective, focusing on nonperturbative QCD as encoded in the functional approach via Dyson-Schwinger and Bethe-Salpeter equations. We give a systematic overview as to how results are obtained in this framework and explain technical connections to lattice QCD. We also discuss the mutual relations to the quark model, which still serves as a reference to distinguish 'expected' from 'unexpected' physics. We confront recent results on the spectrum of non-strange and strange baryons, their form factors and the issues of two-photon processes and Compton scattering determined in the DysonSchwinger framework with those of lattice QCD and the available experimental data. The general aim is to identify the underlying physical mechanisms behind the plethora of observable phenomena in terms of the underlying quark and gluon degrees of freedom.

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“…10 −3 /m π , found in the SAID [10], MAID [9], and Bonn-Gatchina [11] fits. As a test, this parameter was fixed and the remaining multipoles varied.…”

Section: Introductionmentioning

confidence: 99%

Single-energy amplitudes for pion photoproduction in the first resonance region

Workman

2011

Phys. Rev. C

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We consider multipole amplitudes for low-energy pion photoproduction, constructed with minimal model dependence, at single energies. A previous fit making minimal use of Watson's theorem has been reexamined in light of more recent measurements. Problems associated with the choice of a unique solution are discussed. Comparisons with more recent fits to the full resonance region are made. Explanations are suggested for the discrepancies and more precise measurements of the recoil polarization, P , are motivated.

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Analysis of pion photoproduction data

Cited by 254 publications

References 59 publications

Electroexcitation of nucleon resonances from CLAS data on single pion electroproduction

Electroexcitation of nucleon resonances from CLAS data on single pion electroproduction

Baryons as relativistic three-quark bound states

Single-energy amplitudes for pion photoproduction in the first resonance region

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