Partial-wave analysis of pion photoproduction

Arndt, Richard A.; Workman, R. L.; Li, Zhujun; Roper, L. David

doi:10.1103/physrevc.42.1853

Cited by 102 publications

(105 citation statements)

References 16 publications

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“…In inclusive electron scattering data [10] a P 11 resonance has not been observed; however, in γ -induced processes it is rather small but clearly observed (see, e.g. [11]). In an attempt to understand the different results, a T-matrix description of α-p, π-N , and γ -p has been performed [12], which shows that all data can be described consistently by assuming two structures in this resonance, a strong scalar monopole excitation (Saturne resonance) interpreted as the breathing mode of the nucleon, and a second much wider structure, which can be interpreted as second order excitation (spin-isospin (M1) mode).…”

Section: Introductionmentioning

confidence: 99%

Structure of the breathing mode of the nucleon from high-energyp−pscattering

Morsch

Żuprański

2005

Phys. Rev. C

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Spectra of p-p and π -p scattering at beam momenta between 6 and 30 GeV/c have been reanalyzed. These show strong excitation of N * resonances, the strongest one corresponding to the "scalar" P 11 excitation (breathing mode) at m 0 = 1400 ± 10 MeV with = 200 ± 20 MeV. The result of a strong scalar excitation is supported by a large longitudinal amplitude S 1/2 extracted from e-p scattering. From exclusive data on p + p → ppπ + π − , a large 2π -N decay branch for the P 11 resonance of B 2π = 75 ± 20% has been extracted.The differential cross sections were described in a double-folding approach, assuming multigluon exchange as the dominant part of the effective interaction between the constituents of projectile and target. First, the parameters of the interaction were fitted to elastic scattering; then, with this interaction, the inelastic cross sections were described in the distorted wave Born approximation (DWBA). A good description of the data requires a surface peaked transition density, quite different from that of a pure radial mode. In contrast, the electron scattering amplitude S 1/2 is quite well described by a breathing mode transition density with radial node. This large difference between charge and matter transition densities suggests that in p-p scattering the coupling to the multigluon field is much more important than the coupling to the valence quarks. A multigluon (or sea-quark) transition density is derived, which also shows breathing, indicating a rather complex multiquark structure of N and N * including additional multigluon (or q 2nq 2n ) creation out of the ground state vacuum.

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Section: Introductionmentioning

confidence: 99%

Structure of the breathing mode of the nucleon from high-energyp−pscattering

Morsch

Żuprański

2005

Phys. Rev. C

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“…(30), B π is the single-pion branching ratio of the resonance N * andΓ π (W ) the energy-dependent pionic width [31], while the inelastic widthΓ inel (W ) of the decays N * → (ππN, ηN, πππN, ..) is parametrized as in Ref.…”

Section: S-channel Dispersion Integralmentioning

confidence: 99%

“…In this approximation, we first calculate the resonant part of the pion photoproduction multipoles using the Breit-Wigner parametrization of Ref. [31], which is then scaled by a suitable factor to include the inelastic decays of the resonances. The resulting contribution to Im s A i is…”

Section: S-channel Dispersion Integralmentioning

confidence: 99%

Fixed-tsubtracted dispersion relations for Compton scattering off the nucleon

et al. 1999

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We present fixed-t subtracted dispersion relations for Compton scattering off the nucleon at energies E γ ≤ 500 MeV, as a formalism to extract the nucleon polarizabilities with a minimum of model dependence. The subtracted dispersion integrals are mainly saturated by πN intermediate states in the s-channel γN → πN → γN and ππ intermediate states in the t-channel γγ → ππ → NN . For the subprocess γγ → ππ, we construct a unitarized amplitude and find a good description of the available data. We show results for Compton scattering using the subtracted dispersion relations and display the sensitivity on the scalar polarizability difference α − β and the backward spin polarizability γ π , which enter directly as fit parameters in the present formalism.

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“…From the above relations one can see that the the amplitude phases cannot be accessed from the data on differential cross section alone and that the only source of information to determine them are the polarisation asymmetries. The combined study of the unpolarised cross section and of the polarisation asymmetries is critical in order to get access to the production amplitudes from the experimental data, and the interference among the helicity amplitudes can play a crucial role in revealing subtle effects [17].…”

mentioning

confidence: 99%

First measurement of the $\Sigma$ beam asymmetry in $\eta^{\prime}$ photoproduction off the proton near threshold

et al. 2015

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Abstract. The Σ beam asymmetry in η photoproduction off the proton was measured at the GrAAL polarised photon beam with incoming photon energies of 1.461 and 1.480 GeV. For both energies the asymmetry as a function of the meson production angle shows a clear structure, more pronounced at the lowest one, with a change of sign around 90• . The observed behaviour is compatible with P -wave D-wave (or S-wave F -wave) interference, the closer to threshold the stronger. The results are compared to the existing state-of-the-art calculations that fail to account for the data.The experimental study of nucleon excited states is fundamental for the understanding of its internal structure. Important differences are still observed today be- . Recent reports on advances in the experimental studies of the excited nucleon state spectrum can be found in [9,10].Several states predicted by these models have not been observed (missing resonances). The nucleon excited states decay strongly with meson emission; therefore meson photoproduction experiments off the nucleon are an ideal way of searching for missing resonances and complement the information obtained with pion-nucleon scattering experiments.

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Partial-wave analysis of pion photoproduction

Cited by 102 publications

References 16 publications

Structure of the breathing mode of the nucleon from high-energyp−pscattering

Structure of the breathing mode of the nucleon from high-energyp−pscattering

Fixed-tsubtracted dispersion relations for Compton scattering off the nucleon

First measurement of the $\Sigma$ beam asymmetry in $\eta^{\prime}$ photoproduction off the proton near threshold

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