Bulletin of the American Physical Society
2010 Fall Meeting of the APS Division of Nuclear Physics
Volume 55, Number 14
Tuesday–Saturday, November 2–6, 2010; Santa Fe, New Mexico
Session GA: Progress in Baryon Spectroscopy |
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Chair: Curtis Meyer, Carnegie Mellon University Room: Sweeny A |
Friday, November 5, 2010 8:30AM - 9:06AM |
GA.00001: Baryonic spectra from multichannel amplitudes Invited Speaker: Ongoing and future experiments at precision electromagnetic facilities around the world have ushered in a renaissance in hadronic reaction theory. These high-statistics experiments offer comprehensive kinematic coverage and a large number of new polarization observables -- including the exciting prospect of a complete measurement for several reactions -- and will provide stringent constraints on reaction parameterizations and models. The recent developments promise to shed new light on the physics of baryon resonance spectroscopy, providing a window into the non-perturbative regime of QCD. Though the reaction theory is a mature field, complex phenomenological and theoretical challenges remain. Phenomenologically, amplitudes must be determined in a manner consistent with unitarity while fitting a multichannel set of unpolarized and polarized observables. The {\sc said} amplitudes for $\pi N\to\pi N$ and $\pi N\to\eta N$, as a model example of such a phenomenology, are discussed in some detail and compared with other parameterizations. Efforts to enlarge the said approach to describe the photo- and hadro-production globally have recently yielded promising developments, including a simultaneous description of $\pi-$ and $\eta-$ photoproduction amplitudes. Theoretically, multichannel, unitary dynamical models have recently undergone significant developments. An overview of these approaches are considered by comparing results from several recent calculations. [Preview Abstract] |
Friday, November 5, 2010 9:06AM - 9:42AM |
GA.00002: The Experimental Status of Baryon Resonances Invited Speaker: Nucleons are complex systems of confined quarks and exhibit characteristic spectra of excited states. Highly excited nucleon states are sensitive to details of quark confinement which is poorly understood within Quantum Chromodynamics (QCD), the fundamental theory of strong interactions. Thus, measurements of excited nucleon states and the corresponding determination of their properties are needed to come to a better understanding of how confinement works in nucleons. However, the excited states of the nucleon cannot simply be inferred from cleanly separated spectral lines. Quite the contrary, a {\it spectral analysis} in nucleon resonance physics is challenging because of the fact that these resonances are broadly overlapping states which decay into a multitude of final states involving mesons and baryons. To provide a consistent and complete picture of an individual nucleon resonance, the various possible production and decay channels must eventually be treated in a multi-channel framework that permits separating resonance from background contributions. A long-standing question in hadron physics is whether the large number of so-called {\it missing} baryon resonances really exists, i.e. experimentally not established baryon states which are predicted by quark models based on three constituent quark effective degrees of freedom. It is important to emphasize that nearly all existing data on non-strange production of baryon resonances result from $\pi N$ scattering experiments. However, quark models predict strong couplings of these {\it missing} states to $\gamma p$ rendering the study of these resonances in photo-induced reactions a very promising approach. Several new states have in fact been proposed in recent experiments. Current and upcoming experiments at Jefferson Laboratory will determine polarization (or spin) observables for photoproduction processes involving baryon resonances. Differences between the predictions for these observables can be large, and so conversely they provide strong constraints on the analysis. An interesting question is whether it is possible to design a complete set of experiments which will uniquely determine the scattering amplitude for a given process. The current effort with the CLAS detector at Jefferson Lab is to utilize highly-polarized frozen-spin (butanol) and deuterium targets in combination with polarized photon beams. In particular, the very successful FROST experiment took the first double-polarization data from November '07 to February '08 paving the way for a {\it complete experiment} in $K\Lambda$ and $K\Sigma$ photoproduction. This contribution will review recent results and also discuss open questions and perspectives in $N^\ast$ physics. [Preview Abstract] |
Friday, November 5, 2010 9:42AM - 10:18AM |
GA.00003: Excited State Spectroscopy from Lattice QCD Invited Speaker: There has been a resurgence of interest in spectroscopy with a new generation of experiments that are starting worldwide, for example BES III, GSI/Panda, and Jefferson Lab's GlueX project as well as CLAS12. Spectroscopy reveals fundamental aspects of hadronic physics. However, the excited spectrum of light quark mesons and baryons is not well determined nor understood. Lattice QCD is quite amenable to such non-perturbative studies, but there are many challenges. I will report on some recent progress that has been made in determining the highly excited spectrum of QCD, and point out challenges for future work. [Preview Abstract] |
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