Unravelling the Excitation Spectrum of the Nucleon

Sandorfi, A. M.

doi:10.1088/1742-6596/424/1/012001

Cited by 7 publications

(9 citation statements)

References 20 publications

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“…More data of the polarization observables of γp → K + Λ will soon become available from JLab and other photon/electron beam facilities. Actually, all of the 15 possible polarization observables for this reaction have already been measured at CLAS [48].…”

Section: B γN → πNmentioning

confidence: 99%

Nucleon resonances within a dynamical coupled-channels model ofπNandγNreactions

et al. 2013

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The nucleon resonances are investigated within a dynamical coupled-channels model of πN and γN reactions up to the invariant mass W = 2 GeV. The meson-baryon (M B) channels included in the calculations are M B = πN , ηN , KΛ, KΣ, and ππN that has π∆, ρN , and σN resonant components. From the extracted residues, we have determined the N * → πN, γN, ηN, KΛ, KΣ transition amplitudes at resonance poles. We compare the resonance pole positions from our analysis with those given by the Particle Data Group and the recent coupled-channels analyses by the Jülich and Bonn-Gatchina groups. Four results agree well only for the first N * in each spin-parity-isospin (J P , I) channel. For higher mass states, the number of states and their resonance positions from four results do not agree well. We discuss the possible sources of the discrepancies and the need of additional data from new hadron facilities such as J-PARC.

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Section: B γN → πNmentioning

confidence: 99%

Nucleon resonances within a dynamical coupled-channels model ofπNandγNreactions

et al. 2013

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“…The photon beam irradiated the production target. Unpolarized liquid hydrogen or deuterium or the newly developed polarized frozenspin (FROST) [6] or HDice targets [7,8] have been used in these experiments. Finalstate particles were detected in the CEBAF Large Acceptance Spectrometer (CLAS) [9].…”

Section: Introductionmentioning

confidence: 99%

Baryon Spectroscopy with Polarization Observables from CLAS

Strauch

2016

Few-Body Syst

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The spectrum of nucleon excitations is dominated by broad and overlapping resonances. Polarization observables in photoproduction reactions are key in the study of these excitations. They give indispensable constraints to partial-wave analyses and help clarify the spectrum. A series of polarized photoproduction experiments have been performed at the Thomas Jefferson National Accelerator Facility with the CEBAF Large Acceptance Spectrometer (CLAS). These measurements include data with linearly and circularly polarized tagged-photon beams, longitudinally and transversely polarized proton and deuterium targets, and recoil polarizations through the observation of the weak decay of hyperons. An overview of these studies and recent results will be given.The nucleon is a color-neutral object which consists of color-charged quarks and gluons. Quantum chromodynamics (QCD) is the fundamental theory of the strong interaction between quarks and gluons. Valuable information about QCD can be learned from nuclear spectroscopy; e.g. information about the internal degrees of freedom in a nucleon. Experiments, especially pion-nucleon scattering, have confirmed low-lying excited states predicted by quark models with three independent quark degrees of freedom. These models, however, predict an overabundance of higher-lying excited states compared to what has been observed until now [1]. Also, recent lattice QCD calculations [2] find a large number of not-yet-discovered nucleon resonances. To clarify the nucleon resonance spectrum is an important task in the study of QCD.Nucleon resonances are short-lived, and the identification of resonances in partial-wave analyses of experimental data is complicated by their large width and overlap. Experimental cross sections are insufficient, and polarization observables are crucial to constrain these analyses. A complete set of certain polarization observables is necessary to unambiguously determine the amplitudes of the reaction. In the photoproduction of pseudoscalar mesons, a formally complete experiment requires at each energy and angle the measurement of at least eight carefully chosen observables [3]. In the photoproduction of two mesons, even more observables are needed [4]. It is also important to include in the analysis data from a variety of excitation and decay channels, as some of the missing states may couple only weakly to, e.g., the πN channel.

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“…A number of factors complicate the study of excited nucleon states [3]. Most important is the lack of experimental data on the majority of the 16 possible spin matrix elements in pseudoscalar meson photoproduction, which has created ambiguities in PWA [4].…”

Section: Introductionmentioning

confidence: 99%

A portable cryostat for the cold transfer of polarized solid HD targets: HDice-I

Bass

Bade

Blecher

et al. 2014

Nuclear Instruments and Methods in Physics Research Section A:

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A device has been developed with moveable liquid nitrogen and liquid helium volumes that is capable of reaching over two meters into the coldest regions of a cryostat or dilution refrigerator and reliably extracting or installing a target of solid, polarized hydrogen deuteride (HD). This Transfer Cryostat incorporates a cylindrical neodymium rare-earth magnet that is configured as a Halbach dipole, which is maintained at 77 K and produces a 0.1 T field around the HD target. Multiple layers provide a hermetic 77 K-shield as the device is used to maintain a target at 2 K during a transfer between cryostats. Tests with frozen-spin HD show negligible polarization loss for either H or D over typical transfer periods. Multiple target transfers with this apparatus have shown an overall reliability of about 95% per transfer, which is a significant improvement over earlier versions of the device.

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Unravelling the Excitation Spectrum of the Nucleon

Cited by 7 publications

References 20 publications

Nucleon resonances within a dynamical coupled-channels model ofπNandγNreactions

Nucleon resonances within a dynamical coupled-channels model ofπNandγNreactions

Baryon Spectroscopy with Polarization Observables from CLAS

A portable cryostat for the cold transfer of polarized solid HD targets: HDice-I

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